Background: In separate Women's Health Initiative randomized trials, combined hormone therapy with estrogen plus progestin reduced colorectal cancer incidence but estrogen alone in women with hysterectomy did not. We now analyze features of the colorectal cancers that developed and examine the survival of women following colorectal cancer diagnosis in the latter trial.

Participants and Methods: 10,739 postmenopausal women who were 50 to 79 years of age and had undergone hysterectomy were randomized to conjugated equine estrogens (0.625 mg/d) or matching placebo. Colorectal cancer incidence was a component of the monitoring global index of the study but was not a primary study endpoint. Colorectal cancers were verified by central medical record and pathology report review. Bowel exam frequency was not protocol defined, but information on their use was collected.

Results: After a median 7.1 years, there were 58 invasive colorectal cancers in the hormone group and 53 in the placebo group [hazard ratio, 1.12; 95% confidence interval (95% CI), 0.77-1.63]. Tumor size, stage, and grade were comparable in the two randomization groups. Bowel exam frequency was also comparable in the two groups. The cumulative mortality following colorectal cancer diagnosis among women in the conjugated equine estrogen group was 34% compared with 30% in the placebo group (hazard ratio, 1.34; 95% CI, 0.58-3.19).

Conclusions: In contrast to the preponderance of observational studies, conjugated equine estrogens in a randomized clinical trial did not reduce colorectal cancer incidence nor improve survival after diagnosis. (Cancer Epidemiol Biomarkers Prev 2008;17(10):2609–18)

Colorectal cancer is the second leading cause of cancer death in the United States (1). Interventions including calcium (2), celecoxib (3), aspirin (4), sulindac (5, 6), and the bile acid ursodiol (7) have all reduced colorectal polyp recurrence in various high-risk populations. However, only combined estrogen plus progestin use has been shown to reduce colorectal cancer incidence in a randomized trial setting (8, 9).

In prospective cohort studies, which have generally not distinguished combined estrogen plus progestin from estrogen alone use, postmenopausal hormone therapy has been consistently associated with reduced colorectal cancer risk (10-14). In addition, both significantly improved colorectal cancer–specific survival (15), and overall survival (15, 16) has been seen in women using postmenopausal hormone therapy when their colorectal cancer was diagnosed. These observational study findings received some support from the Women's Health Initiative (WHI) randomized trial evaluating combined hormone therapy with conjugated equine estrogen plus medroxyprogesterone acetate, wherein a statistically significant 44% decrease in colorectal cancer incidence in the combined hormone therapy compared with placebo groups was seen (9).

In the original report of the WHI randomized placebo-controlled trial, conjugated equine estrogen alone did not reduce colorectal cancer incidence compared with placebo (17). The current report provides details of the colorectal cancer screening procedures, characteristics of the diagnosed colorectal cancers, additional subgroup analyses, and additional follow-up information, including survival following colorectal cancer diagnosis in the WHI randomized trial comparing conjugated equine estrogen alone to placebo.

Study Design

The WHI trial of conjugated equine estrogen alone enrolled 10,739 women with previous hysterectomy at 40 clinical centers in the United States between 1993 and 1998 under protocols approved by the institutional review boards at each institution (18). Recruitment was predominantly done through mass mailings. Eligibility criteria included ages between 50 to 79 years, postmenopausal status, and providing written informed consent. Women were eligible if they had undergone a previous hysterectomy, with or without oophorectomy. Exclusion criteria included a personal history of breast cancer, medical conditions likely to result in death in the next three years, or colorectal cancer within the past 10 years. Women currently using postmenopausal hormones were eligible after a 3-month washout period.

The trial was a randomized, double-blind, placebo-controlled trial of conjugated equine estrogen (0.625 mg/d) administered in a single tablet (Premarin, Wyeth Ayerst) compared with an identical-seeming placebo. Randomization was determined by the WHI Clinical Coordinating Center and implemented at local centers with a distributed database that maintained blinding of participants and staff to randomization allocation throughout the trial.

Women in the hormone trial also could participate on study entry in the dietary modification trial or could enter a randomized trial of calcium and vitamin D at the first or second annual clinic visit. Approximately 20% and 60% joined the dietary modification and calcium and vitamin D trials, respectively.

Follow-up

Follow-up procedures have been described previously (18, 19). Participants were contacted after six weeks to assess symptoms and promote adherence, at six month intervals for clinical outcomes assessment, and annually for clinic visits. For potential colorectal cancer diagnoses, medical records and pathology reports were reviewed by locally trained physician adjudicators (blind to group assignment) to identify cases; cases underwent a second blind adjudication at the clinical coordinating center and tumor characteristics were coded using the Surveillance, Epidemiology, and End Results program guidelines (20). Proximal colon lesions included those in the cecum, ascending colon (right colon), hepatic flexure, and transverse colon. Distal colon lesions included those in the splenic flexure, descending colon (left colon), and sigmoid and rectosigmoid junction.

Colorectal cancer was not a WHI conjugated equine estrogen primary study outcome and colorectal cancer screening was not protocol defined; participants received bowel exams as determined by their personal health care provider. Self-administered questionnaires or structured telephone interviews were used every six months to monitor the frequencies of rectal exams, fecal occult-blood testings, sigmoidoscopies and colonoscopies (asked as one question), and barium enema exams. Participants were also asked semiannually if they had intestinal or colon polyps diagnosed during that period.

Termination of the Study

After a mean follow-up of 7.1 years, the National Heart, Lung, and Blood Institute stopped the trial early because of increased stroke risk, absence of coronary heart disease benefit, and the low probability that interpretation of the trial would change with further information. In the original report on conjugated equine estrogen trial outcomes, 119 total colorectal cancer cases were identified (17). The current report is based on 120 total colorectal cancers diagnosed before February 29, 2004, the date on which the participants were instructed to discontinue their study medication and follow-up mortality data through April 1, 2005, on those women diagnosed with colorectal cancer.

Statistical Analysis

Primary results were assessed with time-to-event methods based on the intention-to-treat principle. Comparisons of rates of colorectal cancer are presented as hazard ratios with 95% CI and Wald z-statistical P values from Cox regression models, stratified according to age and randomization in the WHI trials of dietary modification, calcium and vitamin D, or both. Because participants in the calcium and vitamin D trial entered that trial one to two years after their entry into the hormone trial, stratification for calcium and vitamin D trial participation was time dependent, based on the calcium and vitamin D randomization date. No adjustments are made for multiple analyses over time because the incidence of colorectal cancer did not influence the decision to stop the trial.

Kaplan-Meier plots were used to examine the rates of colorectal cancer over time. Effects of baseline participant characteristics, including risk factors for colorectal cancer, were assessed in Cox regression models as described above, expanded to include the designated risk factor and randomization assignment (as the main effects) and the interaction between them. P values for interaction were computed with likelihood-ratio tests, and models with and without the interaction term were compared. For variables measured on a continuous scale, P values were computed on the continuous variable. Women with missing risk factor values in a given analysis were excluded from that analysis. Eighteen subgroup comparisons were done; one would be expected to be significant at the 0.05 level by chance alone. The exploratory analyses significance levels were not adjusted for multiple comparisons. Comparisons of survival after colorectal cancer diagnosis between estrogen alone and placebo groups were based on a proportional hazards model that was stratified by age and cancer stage at diagnosis with age as a covariate. Sensitivity analyses were conducted to explore the impact of adherence on outcome, and follow-up was censored six months after participants first became nonadherent (defined as taking <80% of study pills).

There were 5,310 women randomized to conjugated equine estrogen and 5,429 to placebo (total, 10,739) with follow-up during active intervention for an average of 7.1 years (maximum, 10.8 years). Recent outcomes data were available for 10,176 participants (94.8%). Of the women, 54% in the hormone group and 53.5% in the control group stopped study medications at some point; most did not restart. In addition, 5.7% in the hormone group and 9.1% in the control group reported using postmenopausal hormones off protocol. A full consort diagram is published elsewhere (8). The two groups were well balanced for colorectal cancer risk factors, including age, education, anthropometry, personal or family history of colorectal cancer, smoking history, use of anti-inflammatory medications, dietary patterns, use of nutritional supplements, levels of physical activity, previous postmenopausal hormone use, and previous colorectal cancer screening (Table 1).

Table 1.

Characteristics of participants in the WHI conjugated equine estrogen trial at baseline by group assignment

CEE
Placebo
n (%)n (%)
Characteristic   
Age at screening   
    50-59 1,637 (30.8) 1,673 (30.8) 
    60-69 2,387 (45.0) 2,465 (45.4) 
    70-79 1,286 (24.2) 1,291 (23.8) 
Ethnicity   
    White 4,007 (75.5) 4,075 (75.1) 
    Black 782 (14.7) 835 (15.4) 
    Hispanic 322 (6.1) 333 (6.1) 
    American Indian 41 (0.8) 34 (0.6) 
    Asian or Pacific Islander 86 (1.6) 78 (1.4) 
    Unknown 72 (1.4) 74 (1.4) 
Education   
    0-8 y 181 (3.4) 148 (2.7) 
    Some high school 354 (6.7) 370 (6.9) 
    High school diploma or GED 1,233 (23.5) 1,188 (22.1) 
    School after high school 2,271 (43.2) 2,350 (43.7) 
    College degree or higher 1,216 (23.1) 1,327 (24.7) 
First-degree relative with colorectal cancer   
    None 3,904 (85.3) 4,017 (85.2) 
    1 575 (12.6) 591 (12.5) 
    ≥2 98 (2.1) 109 (2.3) 
History of polyps removal   
    No 4,323 (90.4) 4,336 (90.3) 
    Yes 460 (9.6) 466 (9.7) 
History of ulcerative colitis or Crohn disease   
    No 5,145 (98.6) 5,268 (98.8) 
    Yes 74 (1.4) 64 (1.2) 
History of colorectal cancer   
    No 5,233 (99.7) 5,339 (99.6) 
    Yes 16 (0.3) 24 (0.4) 
History of diabetes   
    No 4,806 (90.5) 4,906 (90.4) 
    Yes 502 (9.5) 519 (9.6) 
BMI   
    <25 1,110 (21.0) 1,096 (20.3) 
    25 to <30 1,795 (34.0) 1,912 (35.5) 
    ≥30 2,376 (45.0) 2,383 (44.2) 
Waist circumference > 88 cm   
    No 2,304 (43.5) 2,342 (43.3) 
    Yes 2,994 (56.5) 3,071 (56.7) 
Height > 161.3 cm   
    No 2,633 (49.6) 2,718 (50.1) 
    Yes 2,654 (50.0) 2,688 (49.5) 
Physical activity (Metabolic equivalents per week)   
    None 1,081 (22.2) 1,043 (21.3) 
    >0-3.75 1,089 (22.3) 1,142 (23.3) 
    >3.75-8.75 914 (18.7) 895 (18.3) 
    >8.75-17.5 968 (19.8) 958 (19.5) 
    >17.5 828 (17.0) 866 (17.7) 
NSAID use   
    No 3,601 (67.8) 3,689 (68.0) 
    Yes 1,709 (32.2) 1,740 (32.1) 
Ibuprofen use   
    No 4,702 (88.5) 4,798 (88.4) 
    Yes 608 (11.5) 631 (11.6) 
Aspirin use (≥100 mg)   
    No 4,413 (83.1) 4,498 (82.9) 
    Yes 897 (16.9) 931 (17.2) 
Acetaminophen use   
    No 4,566 (86.0) 4,654 (85.7) 
    Yes 744 (14.0) 775 (14.3) 
Total Energy (kcal)   
    ≤1,119 1,211 (23.9) 1,197 (23.1) 
    >1,119-1,414.5 980 (19.3) 1,056 (20.4) 
    >1,414.5-1,715 957 (18.9) 939 (18.1) 
    >1,715-2,129.5 907 (17.9) 926 (17.9) 
    >2,129.5 1,021 (20.1) 1,056 (20.4) 
Percent energy from fat   
    ≤27 867 (17.1) 868 (16.8) 
    >27-32.5 920 (18.1) 964 (18.6) 
    >32.5-37 1,069 (21.1) 1,098 (21.2) 
    >37-41.5 1,067 (21.0) 1,050 (20.3) 
    >41.5 1,153 (22.7) 1,194 (23.1) 
Selenium (μg/d)   
    ≤74.4 1,813 (35.7) 1,872 (36.2) 
    74.5-106.3 1,596 (31.4) 1,638 (31.7) 
    ≥106.4 1,667 (32.8) 1,664 (32.2) 
Red meat (servings/d)   
    0.000 to <0.364 1,278 (25.2) 1,286 (24.9) 
    0.364 to <0.649 1,272 (25.1) 1,290 (25.0) 
    0.649 to <1.070 1,262 (25.9) 1,293 (25.0) 
    ≥1.070 1,260 (24.8) 1,301 (25.2) 
Fruit and vegetables (servings/d)   
    0.0 to ≤3.0 2,214 (43.6) 2,223 (43.0) 
    3.0 to ≤6.0 2,166 (42.7) 2,195 (42.4) 
    6.0 to ≤9.0 606 (11.9) 625 (12.1) 
    >9.0 92 (1.8) 132 (2.6) 
Alcohol intake   
    None 1,995 (38.0) 2,007 (37.2) 
    <1 drink/wk 1,768 (33.7) 1,815 (33.7) 
    ≥1 drink/wk 1,484 (28.3) 1,566 (29.1) 
Multivitamin use   
    No 3,618 (68.1) 3,683 (67.8) 
    Yes 1,692 (31.9) 1,746 (32.2) 
Calcium supplement use (mg/d)   
    None 3,074 (57.9) 3,041 (56.0) 
    ≤200 887 (16.7) 918 (16.9) 
    >200-662 745 (14.0) 812 (15.0) 
    >662 604 (11.4) 658 (12.1) 
Vitamin D supplement use (μg/d)   
    None 3,290 (62.0) 3,328 (61.3) 
    ≤10 1,696 (31.9) 1,770 (32.6) 
    >10 324 (6.1) 331 (6.1) 
Smoking   
    Never smoked 2,723 (51.9) 2,705 (50.4) 
    Past smoker 1,986 (37.8) 2,089 (38.9) 
    Current smoker 542 (10.3) 571 (10.6) 
Oral contraceptive use, duration   
    Non-user 3,257 (61.4) 3,377 (62.2) 
    <5 y 1,207 (22.8) 1,198 (22.1) 
    5 to <10 y 472 (8.9) 441 (8.1) 
    ≥10 y 369 (7.0) 411 (7.6) 
Previous menopausal hormone use   
    Non-user 2,769 (52.1) 2,770 (51.0) 
    <5 y 1,352 (25.5) 1,412 (26.0) 
    5 to <10 y 469 (8.8) 515 (9.5) 
    ≥10 y 720 (13.6) 732 (13.5) 
Previous E-alone use   
    Non-user 2,872 (54.1) 2,891 (53.3) 
    <5 y 1,317 (24.8) 1,368 (25.2) 
    5 to <10 y 448 (8.4) 494 (9.1) 
    ≥10 y 673 (12.7) 676 (12.5) 
Previous E+progestin use   
    Non-user 5,093 (95.9) 5,178 (95.4) 
    <5 y 144 (2.7) 158 (2.9) 
    5 to <10 y 42 (0.8) 56 (1.0) 
    ≥10 y 31 (0.6) 37 (0.7) 
Recency of HRT use   
    Non-user 2,769 (52.2) 2,770 (51.1) 
    Past, <5 y 566 (10.7) 586 (10.8) 
    Past, 5-10 y 257 (4.8) 271 (5.0) 
    Past, >10 y 1,048 (19.7) 1,091 (20.1) 
    Current 669 (12.6) 708 (13.0) 
Bilateral oophorectomy   
    No 2,973 (60.5) 2,917 (58.0) 
    Yes 1,938 (39.5) 2,111 (42.0) 
Previous colonoscopy, sigmoidoscopy, or flex sig   
    None 2,606 (54.0) 2,609 (53.7) 
    <5 y ago 1,216 (25.2) 1,228 (25.3) 
    ≥5 y ago 1,008 (20.9) 1,024 (21.1) 
CEE
Placebo
n (%)n (%)
Characteristic   
Age at screening   
    50-59 1,637 (30.8) 1,673 (30.8) 
    60-69 2,387 (45.0) 2,465 (45.4) 
    70-79 1,286 (24.2) 1,291 (23.8) 
Ethnicity   
    White 4,007 (75.5) 4,075 (75.1) 
    Black 782 (14.7) 835 (15.4) 
    Hispanic 322 (6.1) 333 (6.1) 
    American Indian 41 (0.8) 34 (0.6) 
    Asian or Pacific Islander 86 (1.6) 78 (1.4) 
    Unknown 72 (1.4) 74 (1.4) 
Education   
    0-8 y 181 (3.4) 148 (2.7) 
    Some high school 354 (6.7) 370 (6.9) 
    High school diploma or GED 1,233 (23.5) 1,188 (22.1) 
    School after high school 2,271 (43.2) 2,350 (43.7) 
    College degree or higher 1,216 (23.1) 1,327 (24.7) 
First-degree relative with colorectal cancer   
    None 3,904 (85.3) 4,017 (85.2) 
    1 575 (12.6) 591 (12.5) 
    ≥2 98 (2.1) 109 (2.3) 
History of polyps removal   
    No 4,323 (90.4) 4,336 (90.3) 
    Yes 460 (9.6) 466 (9.7) 
History of ulcerative colitis or Crohn disease   
    No 5,145 (98.6) 5,268 (98.8) 
    Yes 74 (1.4) 64 (1.2) 
History of colorectal cancer   
    No 5,233 (99.7) 5,339 (99.6) 
    Yes 16 (0.3) 24 (0.4) 
History of diabetes   
    No 4,806 (90.5) 4,906 (90.4) 
    Yes 502 (9.5) 519 (9.6) 
BMI   
    <25 1,110 (21.0) 1,096 (20.3) 
    25 to <30 1,795 (34.0) 1,912 (35.5) 
    ≥30 2,376 (45.0) 2,383 (44.2) 
Waist circumference > 88 cm   
    No 2,304 (43.5) 2,342 (43.3) 
    Yes 2,994 (56.5) 3,071 (56.7) 
Height > 161.3 cm   
    No 2,633 (49.6) 2,718 (50.1) 
    Yes 2,654 (50.0) 2,688 (49.5) 
Physical activity (Metabolic equivalents per week)   
    None 1,081 (22.2) 1,043 (21.3) 
    >0-3.75 1,089 (22.3) 1,142 (23.3) 
    >3.75-8.75 914 (18.7) 895 (18.3) 
    >8.75-17.5 968 (19.8) 958 (19.5) 
    >17.5 828 (17.0) 866 (17.7) 
NSAID use   
    No 3,601 (67.8) 3,689 (68.0) 
    Yes 1,709 (32.2) 1,740 (32.1) 
Ibuprofen use   
    No 4,702 (88.5) 4,798 (88.4) 
    Yes 608 (11.5) 631 (11.6) 
Aspirin use (≥100 mg)   
    No 4,413 (83.1) 4,498 (82.9) 
    Yes 897 (16.9) 931 (17.2) 
Acetaminophen use   
    No 4,566 (86.0) 4,654 (85.7) 
    Yes 744 (14.0) 775 (14.3) 
Total Energy (kcal)   
    ≤1,119 1,211 (23.9) 1,197 (23.1) 
    >1,119-1,414.5 980 (19.3) 1,056 (20.4) 
    >1,414.5-1,715 957 (18.9) 939 (18.1) 
    >1,715-2,129.5 907 (17.9) 926 (17.9) 
    >2,129.5 1,021 (20.1) 1,056 (20.4) 
Percent energy from fat   
    ≤27 867 (17.1) 868 (16.8) 
    >27-32.5 920 (18.1) 964 (18.6) 
    >32.5-37 1,069 (21.1) 1,098 (21.2) 
    >37-41.5 1,067 (21.0) 1,050 (20.3) 
    >41.5 1,153 (22.7) 1,194 (23.1) 
Selenium (μg/d)   
    ≤74.4 1,813 (35.7) 1,872 (36.2) 
    74.5-106.3 1,596 (31.4) 1,638 (31.7) 
    ≥106.4 1,667 (32.8) 1,664 (32.2) 
Red meat (servings/d)   
    0.000 to <0.364 1,278 (25.2) 1,286 (24.9) 
    0.364 to <0.649 1,272 (25.1) 1,290 (25.0) 
    0.649 to <1.070 1,262 (25.9) 1,293 (25.0) 
    ≥1.070 1,260 (24.8) 1,301 (25.2) 
Fruit and vegetables (servings/d)   
    0.0 to ≤3.0 2,214 (43.6) 2,223 (43.0) 
    3.0 to ≤6.0 2,166 (42.7) 2,195 (42.4) 
    6.0 to ≤9.0 606 (11.9) 625 (12.1) 
    >9.0 92 (1.8) 132 (2.6) 
Alcohol intake   
    None 1,995 (38.0) 2,007 (37.2) 
    <1 drink/wk 1,768 (33.7) 1,815 (33.7) 
    ≥1 drink/wk 1,484 (28.3) 1,566 (29.1) 
Multivitamin use   
    No 3,618 (68.1) 3,683 (67.8) 
    Yes 1,692 (31.9) 1,746 (32.2) 
Calcium supplement use (mg/d)   
    None 3,074 (57.9) 3,041 (56.0) 
    ≤200 887 (16.7) 918 (16.9) 
    >200-662 745 (14.0) 812 (15.0) 
    >662 604 (11.4) 658 (12.1) 
Vitamin D supplement use (μg/d)   
    None 3,290 (62.0) 3,328 (61.3) 
    ≤10 1,696 (31.9) 1,770 (32.6) 
    >10 324 (6.1) 331 (6.1) 
Smoking   
    Never smoked 2,723 (51.9) 2,705 (50.4) 
    Past smoker 1,986 (37.8) 2,089 (38.9) 
    Current smoker 542 (10.3) 571 (10.6) 
Oral contraceptive use, duration   
    Non-user 3,257 (61.4) 3,377 (62.2) 
    <5 y 1,207 (22.8) 1,198 (22.1) 
    5 to <10 y 472 (8.9) 441 (8.1) 
    ≥10 y 369 (7.0) 411 (7.6) 
Previous menopausal hormone use   
    Non-user 2,769 (52.1) 2,770 (51.0) 
    <5 y 1,352 (25.5) 1,412 (26.0) 
    5 to <10 y 469 (8.8) 515 (9.5) 
    ≥10 y 720 (13.6) 732 (13.5) 
Previous E-alone use   
    Non-user 2,872 (54.1) 2,891 (53.3) 
    <5 y 1,317 (24.8) 1,368 (25.2) 
    5 to <10 y 448 (8.4) 494 (9.1) 
    ≥10 y 673 (12.7) 676 (12.5) 
Previous E+progestin use   
    Non-user 5,093 (95.9) 5,178 (95.4) 
    <5 y 144 (2.7) 158 (2.9) 
    5 to <10 y 42 (0.8) 56 (1.0) 
    ≥10 y 31 (0.6) 37 (0.7) 
Recency of HRT use   
    Non-user 2,769 (52.2) 2,770 (51.1) 
    Past, <5 y 566 (10.7) 586 (10.8) 
    Past, 5-10 y 257 (4.8) 271 (5.0) 
    Past, >10 y 1,048 (19.7) 1,091 (20.1) 
    Current 669 (12.6) 708 (13.0) 
Bilateral oophorectomy   
    No 2,973 (60.5) 2,917 (58.0) 
    Yes 1,938 (39.5) 2,111 (42.0) 
Previous colonoscopy, sigmoidoscopy, or flex sig   
    None 2,606 (54.0) 2,609 (53.7) 
    <5 y ago 1,216 (25.2) 1,228 (25.3) 
    ≥5 y ago 1,008 (20.9) 1,024 (21.1) 

NOTE: From χ2 test.

Abbreviations: CEE, conjugated equine estrogen; E, estrogen; NSAID, nonsteroidal anti-inflammatory drug; HRT, hormone replacement therapy.

At the termination of the study intervention, 53.8% of women had already stopped taking study medication and the discontinuation rate was closely comparable in the intervention and placebo groups. Nonprotocol hormone therapy was initiated by 9.1% in the placebo group and 5.7% in the conjugated equine estrogen group through year 6.

Among the 120 women with colorectal cancer, three in the intervention group and two in the placebo group had stage 0 (in situ) disease. There was one squamous cell carcinoma and one neuroendocrine carcinoma in the placebo group, and one malignant melanoma of the colon and one neuroendocrine carcinoma in the hormone group. All presented analyses are limited to the remaining 111 women with invasive colorectal carcinomas of epithelial origin.

By an intention-to-treat analysis, there was no difference between groups in the incidence of invasive colorectal cancer (58 in the conjugated equine estrogen group and 53 in the placebo group; hazard ratio, 1.12; 95% CI, 0.77-1.63; P = 0.55; Table 2). Although fewer rectal cancers were diagnosed in the conjugated equine estrogen group, a total of only 15 rectal cancers were observed, precluding reliable estimation of any conjugated equine estrogen effect. In addition, Kaplan-Meier plots by randomization group revealed no time trends of treatment effects (Fig. 1). In adherence-adjusted sensitivity analysis, the hazard ratio for invasive colorectal cancer changed only slightly to 1.02 (95% CI, 0.64-1.64). Tumor characteristics were also comparable between treatment groups (Table 2).

Table 2.

Incidence (annualized rate) and characteristics of colorectal cancer, according to hormone treatment group

Tumor characteristicsCEE (n = 5,310)
Placebo (n = 5,429)
Hazard ratio95% CIP
n% (rate)n% (rate)
Invasive colorectal cancer 58 0.15 53 0.14 1.12 0.77-1.63 0.55 
    Colon cancer 53 0.14 43 0.11 1.26 0.84-1.88 0.26 
    Rectal cancer 0.01 10 0.03 0.53 0.18-1.56 0.25 
Histology        
    Adenocarcinoma 51 0.14% 50 0.13% 1.04 0.71-1.54 0.83 
    Mucinous and serous 0.02% 0.01% 2.44 0.63-9.43 0.20 
Tumor grade        
    Missing 0.01% 0.01% Not determined   
    Well differentiated 10 0.03% 0.01% 2.53 0.79-8.07 0.12 
    Moderately differentiated 36 0.10% 37 0.10% 1.00 0.63-1.58 0.99 
    Poorly differentiated or anaplastic 10 0.03% 10 0.03% 1.03 0.43-2.49 0.94 
Stage of disease        
    Localized 19 0.05% 19 0.05% 1.02 0.54-1.93 0.95 
    Regional 34 0.09% 24 0.06% 1.46 0.87-2.47 0.15 
    Distant 0.01% 10 0.03% 0.50 0.17-1.46 0.21 
Lymph node involvement        
    Missing 0.02% 0.02% Not determined   
    No 29 0.08% 27 0.07% 1.09 0.64-1.84 0.76 
    Yes 22 0.06% 19 0.05% 1.20 0.65-2.21 0.57 
Cancer location        
    Proximal 27 0.07% 24 0.06% 1.17 0.67-2.03 0.58 
    Distal 26 0.07% 18 0.05% 1.45 0.79-2.64 0.23 
    Unknown 0.00% <.01% Not determined   
    Rectum 0.01% 10 0.03% 0.53 0.18-1.56 0.25 
Tumor size (cm) 38 4.1 ± 2.0 37 4.0 ± 2.4    
    Missing 20 0.05% 17 0.04% Not determined   
    <3.0 0.02% 11 0.03% 0.78 0.31-1.94 0.59 
    3.0-3.9 0.02% 10 0.03% 0.62 0.22-1.70 0.35 
    4.0-5.9 15 0.04% 0.02% 2.15 0.88-5.27 0.10 
    ≥6.0 0.02% 0.02% 1.18 0.46-3.07 0.73 
Number + lymph nodes 49 1.6 ± 3.3 44 0.9 ± 1.8    
    Missing 10 0.03% 0.02% Not determined   
    None 26 0.07% 25 0.06% 1.05 0.61-1.82 0.86 
    1-2 10 0.03% 16 0.04% 0.65 0.30-1.44 0.29 
    ≥3 12 0.03% 0.01% 4.06 1.15-14.40 0.03 
Tumor characteristicsCEE (n = 5,310)
Placebo (n = 5,429)
Hazard ratio95% CIP
n% (rate)n% (rate)
Invasive colorectal cancer 58 0.15 53 0.14 1.12 0.77-1.63 0.55 
    Colon cancer 53 0.14 43 0.11 1.26 0.84-1.88 0.26 
    Rectal cancer 0.01 10 0.03 0.53 0.18-1.56 0.25 
Histology        
    Adenocarcinoma 51 0.14% 50 0.13% 1.04 0.71-1.54 0.83 
    Mucinous and serous 0.02% 0.01% 2.44 0.63-9.43 0.20 
Tumor grade        
    Missing 0.01% 0.01% Not determined   
    Well differentiated 10 0.03% 0.01% 2.53 0.79-8.07 0.12 
    Moderately differentiated 36 0.10% 37 0.10% 1.00 0.63-1.58 0.99 
    Poorly differentiated or anaplastic 10 0.03% 10 0.03% 1.03 0.43-2.49 0.94 
Stage of disease        
    Localized 19 0.05% 19 0.05% 1.02 0.54-1.93 0.95 
    Regional 34 0.09% 24 0.06% 1.46 0.87-2.47 0.15 
    Distant 0.01% 10 0.03% 0.50 0.17-1.46 0.21 
Lymph node involvement        
    Missing 0.02% 0.02% Not determined   
    No 29 0.08% 27 0.07% 1.09 0.64-1.84 0.76 
    Yes 22 0.06% 19 0.05% 1.20 0.65-2.21 0.57 
Cancer location        
    Proximal 27 0.07% 24 0.06% 1.17 0.67-2.03 0.58 
    Distal 26 0.07% 18 0.05% 1.45 0.79-2.64 0.23 
    Unknown 0.00% <.01% Not determined   
    Rectum 0.01% 10 0.03% 0.53 0.18-1.56 0.25 
Tumor size (cm) 38 4.1 ± 2.0 37 4.0 ± 2.4    
    Missing 20 0.05% 17 0.04% Not determined   
    <3.0 0.02% 11 0.03% 0.78 0.31-1.94 0.59 
    3.0-3.9 0.02% 10 0.03% 0.62 0.22-1.70 0.35 
    4.0-5.9 15 0.04% 0.02% 2.15 0.88-5.27 0.10 
    ≥6.0 0.02% 0.02% 1.18 0.46-3.07 0.73 
Number + lymph nodes 49 1.6 ± 3.3 44 0.9 ± 1.8    
    Missing 10 0.03% 0.02% Not determined   
    None 26 0.07% 25 0.06% 1.05 0.61-1.82 0.86 
    1-2 10 0.03% 16 0.04% 0.65 0.30-1.44 0.29 
    ≥3 12 0.03% 0.01% 4.06 1.15-14.40 0.03 

NOTE: Cox regression models stratified according to age groups, dietary modification participation, and previous colorectal cancer. Calcium and vitamin D participation is adjusted as a time-dependent covariate.

Figure 1.

Invasive colorectal incidence by randomization group.

Figure 1.

Invasive colorectal incidence by randomization group.

Close modal

Among the 18 interactions examined, history of polyp removal, height, and waist circumference differed at the 0.05 level of significance (Table 3) with more colorectal cancer seen in the conjugated equine estrogen group among women with waist circumference of <85 cm or height of <158.7 cm. Although the interaction test was not significant, the hazard ratio of the conjugated equine estrogen to placebo group for invasive colorectal cancer was 0.82 (95% CI, 0.34-1.98) for women 50 to 59 years and 0.83 (95% CI, 0.49-1.43) for women 60 to 69 years old at baseline compared with 2.11 (95% CI, 1.06-4.21) in the 70 to 79 year age group.

Table 3.

Incidence (annualized rate) of invasive colorectal cancer, according to baseline characteristics and treatment group

VariableCEE alonePlaceboHazard ratio* (95% CI)P value for interaction
Number of women (annualized %)     
Overall 58 (0.15%) 53 (0.14%) 1.12 (0.77,1.63)  
Age at enrollment (y)    0.08 
    50-59 9 (0.07%) 11 (0.09%) 0.82 (0.34,1.98)  
    60-69 24 (0.14%) 30 (0.17%) 0.83 (0.49,1.43)  
    70-79 25 (0.29%) 12 (0.13%) 2.11 (1.06,4.21)  
Race or ethnic group    0.40 
    White 46 (0.16%) 39 (0.13%) 1.20 (0.79,1.85)  
    Black 5 (0.09%) 6 (0.10%) 0.92 (0.28,3.02)  
    Hispanic 4 (0.18%) 5 (0.22%) 0.66 (0.17,2.56)  
American Indians 1 (0.36%) 0 (0.00%) ND  
    Asian or Pacific Islander 2 (0.36%) 1 (0.18%) 1.04 (0.06,16.60)  
    Unknown or other 0 (0.00%) 2 (0.39%) ND  
History of polyp removal    0.00 
    No 40 (0.13%) 46 (0.15%) 0.87 (0.57,1.33)  
    Yes 9 (0.29%) 0 (0.00%) ND  
Family history of colorectal cancer    0.10 
    No 41 (0.15%) 45 (0.16%) 0.94 (0.62,1.44)  
    Yes 13 (0.23%) 6 (0.10%) 2.16 (0.82,5.72)  
BMI    0.09 
    <25 18 (0.23%) 9 (0.11%) 2.02 (0.91,4.50)  
    25-29 19 (0.15%) 18 (0.13%) 1.11 (0.58,2.11)  
    ≥30 21 (0.12%) 26 (0.15%) 0.80 (0.45,1.42)  
Height (cm)    0.03 
    96.0-158.6 26 (0.21%) 12 (0.10%) 2.12 (1.07,4.19)  
    158.7-163.9 18 (0.15%) 15 (0.12%) 1.27 (0.64,2.52)  
    164.0-188.3 14 (0.11%) 26 (0.20%) 0.57 (0.29,1.10)  
Waist circumference (cm)    0.03 
    37.0-84.9 22 (0.17%) 11 (0.09%) 2.03 (0.98,4.19)  
    85.0-96.9 18 (0.15%) 17 (0.13%) 1.14 (0.59,2.22)  
    97.0-191.6 18 (0.14%) 25 (0.20%) 0.68 (0.37,1.25)  
Smoking status    0.92 
    Never 33 (0.17%) 28 (0.14%) 1.14 (0.69,1.89)  
    Past 20 (0.14%) 19 (0.12%) 1.14 (0.61,2.15)  
    Current 5 (0.13%) 6 (0.15%) 0.94 (0.28,3.12)  
Alcohol intake    0.29 
    None 20 (0.14%) 20 (0.14%) 1.03 (0.55,1.91)  
    <1 drink/wk 22 (0.17%) 12 (0.09%) 1.86 (0.92,3.76)  
    ≥1 drink/wk 16 (0.15%) 19 (0.17%) 0.96 (0.49,1.89)  
Dietary selenium (μg/d)    0.88 
    ≤74.4 21 (0.16%) 18 (0.14%) 1.22 (0.65,2.29)  
    74.5-106.3 18 (0.16%) 13 (0.11%) 1.44 (0.71,2.95)  
    >106.3 19 (0.16%) 17 (0.14%) 1.07 (0.55,2.06)  
Treated diabetes    0.69 
    Never 52 (0.15%) 46 (0.13%) 1.15 (0.77,1.71)  
    Current or past 6 (0.22%) 7 (0.25%) 1.12 (0.36,3.48)  
Use of NSAIDs    0.96 
    No 40 (0.16%) 37 (0.14%) 1.11 (0.71,1.74)  
    Yes 18 (0.15%) 16 (0.13%) 1.18 (0.60,2.33)  
Previous use of menopausal hormones    0.78 
    No 32 (0.16%) 30 (0.15%) 1.07 (0.65,1.76)  
    Yes 26 (0.14%) 23 (0.11%) 1.17 (0.67,2.05)  
Previous use of oral contraceptives    0.90 
    No 38 (0.17%) 34 (0.14%) 1.15 (0.72,1.82)  
    Yes 20 (0.14%) 19 (0.13%) 1.08 (0.57,2.02)  
Bilateral oophorectomy at baseline    0.35 
    No 25 (0.12%) 28 (0.13%) 0.89 (0.52,1.52)  
    Yes 28 (0.21%) 24 (0.16%) 1.25 (0.72,2.16)  
VariableCEE alonePlaceboHazard ratio* (95% CI)P value for interaction
Number of women (annualized %)     
Overall 58 (0.15%) 53 (0.14%) 1.12 (0.77,1.63)  
Age at enrollment (y)    0.08 
    50-59 9 (0.07%) 11 (0.09%) 0.82 (0.34,1.98)  
    60-69 24 (0.14%) 30 (0.17%) 0.83 (0.49,1.43)  
    70-79 25 (0.29%) 12 (0.13%) 2.11 (1.06,4.21)  
Race or ethnic group    0.40 
    White 46 (0.16%) 39 (0.13%) 1.20 (0.79,1.85)  
    Black 5 (0.09%) 6 (0.10%) 0.92 (0.28,3.02)  
    Hispanic 4 (0.18%) 5 (0.22%) 0.66 (0.17,2.56)  
American Indians 1 (0.36%) 0 (0.00%) ND  
    Asian or Pacific Islander 2 (0.36%) 1 (0.18%) 1.04 (0.06,16.60)  
    Unknown or other 0 (0.00%) 2 (0.39%) ND  
History of polyp removal    0.00 
    No 40 (0.13%) 46 (0.15%) 0.87 (0.57,1.33)  
    Yes 9 (0.29%) 0 (0.00%) ND  
Family history of colorectal cancer    0.10 
    No 41 (0.15%) 45 (0.16%) 0.94 (0.62,1.44)  
    Yes 13 (0.23%) 6 (0.10%) 2.16 (0.82,5.72)  
BMI    0.09 
    <25 18 (0.23%) 9 (0.11%) 2.02 (0.91,4.50)  
    25-29 19 (0.15%) 18 (0.13%) 1.11 (0.58,2.11)  
    ≥30 21 (0.12%) 26 (0.15%) 0.80 (0.45,1.42)  
Height (cm)    0.03 
    96.0-158.6 26 (0.21%) 12 (0.10%) 2.12 (1.07,4.19)  
    158.7-163.9 18 (0.15%) 15 (0.12%) 1.27 (0.64,2.52)  
    164.0-188.3 14 (0.11%) 26 (0.20%) 0.57 (0.29,1.10)  
Waist circumference (cm)    0.03 
    37.0-84.9 22 (0.17%) 11 (0.09%) 2.03 (0.98,4.19)  
    85.0-96.9 18 (0.15%) 17 (0.13%) 1.14 (0.59,2.22)  
    97.0-191.6 18 (0.14%) 25 (0.20%) 0.68 (0.37,1.25)  
Smoking status    0.92 
    Never 33 (0.17%) 28 (0.14%) 1.14 (0.69,1.89)  
    Past 20 (0.14%) 19 (0.12%) 1.14 (0.61,2.15)  
    Current 5 (0.13%) 6 (0.15%) 0.94 (0.28,3.12)  
Alcohol intake    0.29 
    None 20 (0.14%) 20 (0.14%) 1.03 (0.55,1.91)  
    <1 drink/wk 22 (0.17%) 12 (0.09%) 1.86 (0.92,3.76)  
    ≥1 drink/wk 16 (0.15%) 19 (0.17%) 0.96 (0.49,1.89)  
Dietary selenium (μg/d)    0.88 
    ≤74.4 21 (0.16%) 18 (0.14%) 1.22 (0.65,2.29)  
    74.5-106.3 18 (0.16%) 13 (0.11%) 1.44 (0.71,2.95)  
    >106.3 19 (0.16%) 17 (0.14%) 1.07 (0.55,2.06)  
Treated diabetes    0.69 
    Never 52 (0.15%) 46 (0.13%) 1.15 (0.77,1.71)  
    Current or past 6 (0.22%) 7 (0.25%) 1.12 (0.36,3.48)  
Use of NSAIDs    0.96 
    No 40 (0.16%) 37 (0.14%) 1.11 (0.71,1.74)  
    Yes 18 (0.15%) 16 (0.13%) 1.18 (0.60,2.33)  
Previous use of menopausal hormones    0.78 
    No 32 (0.16%) 30 (0.15%) 1.07 (0.65,1.76)  
    Yes 26 (0.14%) 23 (0.11%) 1.17 (0.67,2.05)  
Previous use of oral contraceptives    0.90 
    No 38 (0.17%) 34 (0.14%) 1.15 (0.72,1.82)  
    Yes 20 (0.14%) 19 (0.13%) 1.08 (0.57,2.02)  
Bilateral oophorectomy at baseline    0.35 
    No 25 (0.12%) 28 (0.13%) 0.89 (0.52,1.52)  
    Yes 28 (0.21%) 24 (0.16%) 1.25 (0.72,2.16)  
*

Cox regression models are stratified according to age groups, dietary modification participation, and previous colorectal cancer. Calcium and vitamin D participation is adjusted as a time-dependent covariate.

Test of linear trend is used for age, BMI, height, and waist circumference.

P value for interaction derived from exact test under conditional logistic regression model.

Based on self-reports, the proportion of women who developed polyps during the trial was comparable between the two randomization groups (16.9% of hormone and 17.1% of placebo users) as was the time to first report of an identified polyp (hazard ratio, 0.97; 95% CI, 0.87-1.07). A higher risk for invasive colorectal cancer was associated with previous polyp removal among those in the hormone compared with the control group; however, the limited number of cases (n = 9) precludes reliable estimation of effect (Table 3).

The frequency of bowel exams, including rates of hemoccult testing, rectal exams, and sigmoidoscopy or colonoscopy, was similar in the conjugated equine estrogen and placebo groups during the study. Screening rates increased during the study, with rates of sigmoidoscopy or colonoscopy ranging from ∼9% to 15.5% per year and other exams (rectal or hemoccult) ranging from ∼16% to 23%. Over the study period, 24.0% of women in the hormone group and 22.9% of the placebo group participants reported no bowel screening. Surveillance sigmoidoscopy or colonoscopy was more frequent in women with previous polyp removal than was screening use of these exams in women without such history (69% versus 44%). Screening with these tests was also more frequent in those with a colorectal cancer family history (57% versus 45%) and somewhat more frequent in women 50 to 59 years old but did not differ by randomization group.

Mortality outcomes for participants who were diagnosed with colorectal cancer were compared between randomization groups. After 3.6 ± 2.7 years (mean ± SD) following a colorectal cancer diagnosis, the cumulative mortality rate for women in the conjugated equine estrogen alone group was 34% (20 of 58 dead) compared with 30% (16 of 53 dead) in the placebo group (hazard ratio, 1.34; 95% CI, 0.58-3.19). Kaplan-Meier plots by randomization group are provided in Fig. 2.

Figure 2.

Survival following diagnosis of invasive colorectal cancer by randomization.

Figure 2.

Survival following diagnosis of invasive colorectal cancer by randomization.

Close modal

In a cross-study comparison, the colorectal cancer annual incidence rates were found to be similar in the placebo groups from the trial of conjugated equine estrogen alone compared with the trial of conjugated equine estrogen plus medroxyprogesterone acetate (0.14% for women in the conjugated equine estrogen alone trial versus 0.16% for women in the conjugated equine estrogen plus medroxyprogesterone acetate trials; P = 0.35 for comparison of incidence between the two placebo groups; ref. 1). Difference between the conjugated equine estrogen plus medroxyprogesterone acetate (9) and conjugated equine estrogen effect on colorectal cancer were explored using a Cox regression model stratified according to cohorts, age, dietary modification participation, history of colorectal cancer, and adjusting for covariates of ethnicity, body mass index (BMI), history of polyp removal, previous colonoscopy or sigmoidoscopy, and family history of colorectal cancer. The ratio of the hazard ratios for the conjugated equine estrogen alone compared with the conjugated equine estrogen plus medroxyprogesterone acetate trial for colorectal cancer incidence was 2.21 (95% CI, 1.29-3.81; P = 0.004), indicating a significant difference in hormone therapy effects in the two trials.

In a randomized, double-blind, placebo-controlled trial, conjugated equine estrogen alone for an average of 7.1 years did not influence invasive colorectal cancer incidence or survival following a colorectal cancer diagnosis in postmenopausal women. No differences were observed in the clinical characteristics of the tumors diagnosed in the conjugated equine estrogen and placebo groups. Colorectal cancer risk factors were balanced between treatment groups, as were examinations for colorectal cancer detection.

The lack of an effect of conjugated equine estrogen alone on colorectal cancer incidence contrasts with the results of the WHI trial of conjugated equine estrogen plus medroxyprogesterone acetate, wherein colorectal cancer incidence was significantly lower in the combined hormone group (9). In the randomized Heart and Estrogen/Progestin Replacement Study fewer colorectal cancers were also seen in women randomized to the conjugated equine estrogen and medroxyprogesterone acetate compared with the placebo groups (hazard ratio, 0.69; 95% CI, 0.32-1.49; not significant; ref. 21).

Although participants in the two WHI trials, one evaluating conjugated equine estrogen plus medroxyprogesterone acetate for women with no previous hysterectomy and one evaluating conjugated equine estrogen alone for women with previous hysterectomy, differed in several baseline characteristics (22), the colorectal cancer annual incidence rates were similar in the placebo groups for the two trials. Thus, differences in participant characteristics do not explain the discrepant findings and suggest progestin may modify the influence of estrogen on colorectal cancer. Because colorectal cancers in the WHI combined hormone therapy trial were diagnosed at a higher stage compared with those diagnosed on placebo, a differential influence on cancer detection in the two studies also cannot be excluded as an explanation.

In the predominance of observational studies, postmenopausal hormone therapy use has been consistently associated with reduced colorectal cancer risk (23, 24) and improved cancer-specific and overall survival in some reports (15, 16, 25). However, the observational study literature about menopausal hormone therapy and colorectal cancer have not commonly considered use of estrogen alone and combined hormone therapy separately. Several case-control studies reported that both estrogen plus progestin, as well as estrogen alone, were associated with lower colorectal cancer risk (12, 26). A recent case-control in the United States found an association with lower colorectal cancer risk only in women using estrogen plus progestin (odds ratio, 0.6; 95% CI, 0.5-0.9) but not those using estrogen alone (odds ratio, 0.9; 95% CI, 0.7-1.1; ref. 13). Similarly, in a Swedish cohort (27) and in the large United Kingdom General Practice Research Database, colorectal cancer risk was lower only in women using estrogen plus progestin but not those using estrogen alone (28). Future observational studies of colorectal cancer should clearly differentiate combined hormone use from estrogen alone.

In the current randomized trial, there was no improvement in the post diagnosis survival for women with colorectal cancers in the conjugated equine estrogen group (n = 58 cases) compared with those diagnosed in the placebo group (n = 53 cases; hazard ratio, 1.34; 95% CI, 0.58-3.19). This result stands in contrast to the recent findings of Chan and colleagues (15), who reported that, for women in the Nurse's Health Study cohort, current users of estrogen at the time of diagnosis of colorectal cancer (n = 235 cases) experienced significantly less colorectal cancer–specific mortality and less overall mortality compared with women who never used hormone therapy before a colorectal cancer diagnosis (multivariate hazard ratio for overall mortality, 0.74; 95% CI, 0.56-0.97). In that observational study experience, 75% of the person-time represented estrogen alone use. Other reports of longer survival for women diagnosed with colorectal cancer when they were receiving menopausal hormone therapy do not provide details about type of hormone therapy received (19, 29). Given the findings from the WHI randomized trial, current evidence does not support clinical use of estrogen to improve outcome of postmenopausal women with diagnosed colorectal cancer.

The biological effects of combined estrogen plus progestin and estrogen alone on malignant processes are complex. Use of estrogen alone increases endometrial proliferation and endometrial cancer risk, whereas the addition of progestin to estrogen largely abrogates the estrogen effects (8, 30). Combined estrogen plus progestin use significantly increased breast cancer risk (31), whereas the use of estrogen alone was associated with a nonsignificant reduction in breast cancer incidence (32). Combined conjugated equine estrogen plus medroxyprogesterone acetate use reduced colorectal cancer incidence in the WHI trial for women with no previous hysterectomy (9), but the use of conjugated equine estrogen alone in the currently reported trial did not influence either colorectal cancer incidence or mortality after diagnosis. Taken together, these results suggest an hypothesis that progestins modulate estrogen effects on malignancy and that their influence is organ specific. Alternatively, progestins and/or estrogens alone could simply have different effects on these three cancer types, but clinical evidence for effects related to progestin alone use are sparse.

Study subgroup analyses suggested that conjugated equine estrogen influence on colorectal cancer may vary according to age. Alternatively, given the limited numbers of women in these subgroup analyses and that the test for interaction was not significant, chance alone may explain the age effects observed. One case-control study (33) reporting on mostly unopposed estrogen use found no association with colorectal cancer risk in younger women, but hormone users with ages 60 to 69 years had a lower colorectal cancer risk relative to non-users. A nominally significant interaction among conjugated equine estrogen alone use and colorectal cancer with both waist circumference and height was seen, along with a suggestion of an interaction with BMI. However, observational studies examining BMI modification of hormone therapy association with colorectal cancer have provided conflicting results (16, 34-38), and relationships among BMI, menopausal hormone therapy, and colorectal cancer risk remain unclear.

Although no effect of conjugated equine estrogen alone on colorectal cancer incidence was seen in the current trial, several mechanisms have been proposed as potential mediators of the favorable effect of combined conjugated equine estrogen plus medroxyprogesterone acetate use on colorectal cancer previously reported (9). These include hormone influences on bile acids, (6) insulin (39), and direct effects on the intestinal epithelium (40, 41).

Strengths of the current study include the randomized double-blind design and the long-term follow-up of a large number of ethnically diverse participants with standardized outcome ascertainment and adjudication. The limited number of colorectal cancers is a constraint, as is the lower-than-anticipated adherence to study medications, which likely dilutes any true effect. Although bowel screening was not protocol defined, the frequency of exams was comparable in the two groups.

In summary, in a randomized placebo-controlled clinical trial in 10,749 postmenopausal women, use of conjugated equine estrogen alone did not reduce colorectal cancer incidence or improve the post diagnosis survival of women with this disease.

Program Office: (National Heart, Lung, and Blood Institute, Bethesda, MD) Barbara Alving, Jacques Rossouw, Linda Pottern, Shari Ludlam, Joan McGowan, Nancy Geller, and Leslie Ford.

Clinical Coordinating Center: (Fred Hutchinson Cancer Research Center, Seattle, WA) Ross Prentice, Garnet Anderson, Andrea LaCroix, Ruth Patterson, Anne McTiernan, Barbara Cochrane, Julie Hunt, Lesley Tinker, Charles Kooperberg, Martin McIntosh, C.Y. Wang, Chu Chen, Deborah Bowen, Alan Kristal, Janet Stanford, Nicole Urban, Noel Weiss, and Emily White; (Wake Forest University School of Medicine, Winston-Salem, NC) Sally Shumaker, Ronald Prineas, and Michelle Naughton; (Medical Research Laboratories, Highland Heights, KY) Evan Stein and Peter Laskarzewski; (San Francisco Coordinating Center, San Francisco, CA) Steven R. Cummings, Michael Nevitt, and Lisa Palermo; (University of Minnesota, Minneapolis, MN) Lisa Harnack; (Fisher BioServices, Rockville, MD) Frank Cammarata and Steve Lindenfelser; (University of Washington, Seattle, WA) Bruce Psaty and Susan Heckbert.

Clinical Centers: (Albert Einstein College of Medicine, Bronx, NY) Sylvia Wassertheil-Smoller, William Frishman, Judith Wylie-Rosett, David Barad, and Ruth Freeman; (Baylor College of Medicine, Houston, TX) Jennifer Hays, Ronald Young, Jill Anderson, Sandy Lithgow, and Paul Bray; (Brigham and Women's Hospital, Harvard Medical School, Boston, MA) JoAnn Manson, J. Michael Gaziano, Claudia Chae, Kathryn Rexrode, and Caren Solomon; (Brown University, Providence, RI) Annlouise R. Assaf, Carol Wheeler, Charles Eaton, and Michelle Cyr; (Emory University, Atlanta, GA) Lawrence Phillips, Margaret Pedersen, Ora Strickland, Margaret Huber, and Vivian Porter; (Fred Hutchinson Cancer Research Center, Seattle, WA) Shirley A.A. Beresford, Vicky M. Taylor, Nancy F. Woods, Maureen Henderson, and Robyn Andersen; (George Washington University, Washington, DC) Judith Hsia, Nancy Gaba, and Joao Ascensao; (Harbor-UCLA Research and Education Institute, Torrance, CA) Rowan Chlebowski, Robert Detrano, Anita Nelson, and Michele Geller; (Kaiser Permanente Center for Health Research, Portland, OR) Evelyn Whitlock, Victor Stevens, and Njeri Karanja; (Kaiser Permanente Division of Research, Oakland, CA) Bette Caan, Stephen Sidney, Geri Bailey, and Jane Hirata; (Medical College of Wisconsin, Milwaukee, WI) Jane Morley Kotchen, Vanessa Barnabei, Theodore A. Kotchen, Mary Ann C. Gilligan, and Joan Neuner; (MedStar Research Institute, Howard University, Washington, DC) Barbara V. Howard, Lucile Adams-Campbell, Lawrence Lessin, Monique Rainford, and Gabriel Uwaifo; (Northwestern University, Chicago/Evanston, IL) Linda Van Horn, Philip Greenland, Janardan Khandekar, Kiang Liu, Carol Rosenberg; (Rush University Medical Center, Chicago, IL) Henry Black, Lynda Powell, and Ellen Mason; Martha Gulati; (Stanford Prevention Research Center, Stanford, CA) Marcia L. Stefanick, Mark A. Hlatky, Bertha Chen, Randall S. Stafford, and Sally Mackey; (State University of New York at Stony Brook, Stony Brook, NY) Dorothy Lane, Iris Granek, William Lawson, Gabriel San Roman, and Catherine Messina; (The Ohio State University, Columbus, OH) Rebecca Jackson, Randall Harris, Electra Paskett, W. Jerry Mysiw, and Michael Blumenfeld; (University of Alabama at Birmingham, Birmingham, AL) Cora E. Lewis, Albert Oberman, James M. Shikany, Monika Safford, and Mona Fouad; (University of Arizona, Tucson/Phoenix, AZ) Cyndi Thomson, Tamsen Bassford, Marcia Ko, Ana Maria Lopez, and Cheryl Ritenbaugh; (University at Buffalo, Buffalo, NY) Jean Wactawski-Wende, Maurizio Trevisan, Ellen Smit, Susan Graham, and June Chang; (University of California at Davis, Sacramento, CA) John Robbins and S. Yasmeen; (University of California at Irvine, Irvine, CA) F. Allan Hubbell, Gail Frank, Nathan Wong, Nancy Greep, and Bradley Monk; (University of California at Los Angeles, Los Angeles, CA) Howard Judd, David Heber, and Robert Elashoff; (University of California at San Diego, LaJolla/Chula Vista, CA) Robert D. Langer, Michael H. Criqui, Gregory T. Talavera, Cedric F. Garland, and Matthew A. Allison; (University of Cincinnati, Cincinnati, OH) Margery Gass and Suzanne Wernke; (University of Florida, Gainesville/Jacksonville, FL) Marian Limacher, Michael Perri, Andrew Kaunitz, R. Stan Williams, and Yvonne Brinson; (University of Hawaii, Honolulu, HI) J. David Curb, Helen Petrovitch, Beatriz Rodriguez, Kamal Masaki, and Santosh Sharma; (University of Iowa, Iowa City/Davenport, IA) Robert Wallace, James Torner, Susan Johnson, Linda Snetselaar, and Jennifer Robinson; (University of Massachusetts/Fallon Clinic, Worcester, MA) Judith Ockene, Milagros Rosal, Ira Ockene, Robert Yood, and Patricia Aronson; (University of Medicine and Dentistry of New Jersey, Newark, NJ) Norman Lasser, Baljinder Singh, Vera Lasser, John Kostis, and Peter McGovern; (University of Miami, Miami, FL) Mary Jo O'Sullivan, Linda Parker, Timothy DeSantis, Diann Fernandez, and Pat Caralis; (University of Minnesota, Minneapolis, MN) Karen L. Margolis, Richard H. Grimm, Mary F. Perron, Cynthia Bjerk, and Sarah Kempainen; (University of Nevada, Reno, NV) Robert Brunner, William Graettinger, Vicki Oujevolk, and Michael Bloch; (University of North Carolina, Chapel Hill, NC) Gerardo Heiss, Pamela Haines, David Ontjes, Carla Sueta, and Ellen Wells; (University of Pittsburgh, Pittsburgh, PA) Lewis Kuller, Jane Cauley, and N. Carole Milas; (University of Tennessee Health Science Center, Memphis, TN) Karen C. Johnson, Suzanne Satterfield, Raymond W. Ke, Stephanie Connelly, and Fran Tylavsky; (University of Texas Health Science Center, San Antonio, TX) Robert Brzyski, Robert Schenken, Jose Trabal, Mercedes Rodriguez-Sifuentes, and Charles Mouton; (University of Wisconsin, Madison, WI) Gloria E. Sarto, Douglas Laube, Patrick McBride, Julie Mares-Perlman, and Barbara Loevinger; (Wake Forest University School of Medicine, Winston-Salem, NC) Denise Bonds, Greg Burke, Robin Crouse, Mara Vitolins, and Scott Washburn; (Wayne State University School of Medicine/Hutzel Hospital, Detroit, MI) Susan Hendrix, Michael Simon, and Gene McNeeley.

Former Principal Investigators and Project Officers: (Baylor College of Medicine) John Foreyt, Ph.D.; (Emory University) Dallas Hall, M.D.; (George Washington University) Valery Miller, M.D.; (Kaiser, Oakland, CA) Robert Hiatt, M.D.; (Kaiser, Portland, OR), Barbara Valanis, Ph.D.; (National Cancer Institute, Bethesda, MD), Carolyn Clifford13

13

Deceased.

; (University of California, Irvine, CA) Frank Meyskens, Jr., M.D.; (University of Cincinnati) James Liu, M.D., and Nelson Watts; (University of Miami) Marianna Baum, Ph.D.; (University of Minnesota) Richard Grimm, M.D.; (University of Nevada) Sandra Daugherty, M.D.13; (University of North Carolina, Chapel Hill, NC) David Sheps, M.D., and Barbara Hulka, M.D.; (University of Tennessee, Memphis, TN) William Applegate, M.D.; (University of Wisconsin) Catherine Allen, Ph.D.13

Dr. Chlebowski is a consultant for Astra-Zeneca Pharmaceuticals LP (Wilmington, DE), Novartis (Basel, Switzerland), Pfizer, Inc. (New York, NY), Eli Lilly and Co. (Indianapolis, IN), and Organon International (Kenilworth, NJ) and has received research support from Eli Lilly and Co. and Organon International. There are no other relationships to disclose.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

1
Jemal A, Siegel R, Ward E, et al. Cancer statistics, 2007.
CA Cancer J Clin
2007
;
57
:
43
–66.
2
Baron JA, Beach M, Mandel JS, et al. Calcium supplements for the prevention of colorectal adenomas.
N Engl J Med
1999
;
340
:
101
–7.
3
Steinbach G, Lynch PM, Phillips RKS, et al. The effect of celecoxib, a cyclooxygenase 2 inhibitor, in familial adenomatous polyposis.
N Engl J Med
2000
;
342
:
1946
–52.
4
Sandler RS, Halabi S, Baron JA, et al. A randomized trial of aspirin to prevent colorectal adenomas in patients with previous colorectal cancer.
N Engl J Med
2003
;
348
:
883
–90. [Erratum, N Engl J Med 2003;348:1939.]
5
Labayle D, Fischer D, Vielh P, et al. Sulindac causes regression of rectal polyps in familial adenomatous polyposis.
Gastroenterology
1991
;
101
:
635
–9.
6
Giardiello FM, Hamilton SR, Krush AJ, et al. Treatment of colonic and rectal adenomas with sulindac in familial adenomatous polyposis.
N Engl J Med
1993
;
328
:
1313
–6.
7
Alberts DS, Martinez ME, Hess LM, et al. Phase III trial of ursodeoxycholic acid to prevent colorectal adenoma recurrence.
J Natl Cancer Inst
2005
;
97
:
846
–53.
8
Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial.
JAMA
2002
;
200
:
321
–33.
9
Chlebowski RT, Wactawski-Wende J, Ritenbaugh C, et al. Estrogen plus progestin and colorectal cancer in postmenopausal women.
N Engl J Med
2004
;
350
:
991
–1004.
10
McMichael AJ, Potter JD. Reproduction, endogenous and exogenous sex hormones, and colon cancer: a review and hypothesis.
J Natl Cancer Inst
1980
;
65
:
1201
–7.
11
La Vecchia C, Gallus S, Fernandez E. Hormone replacement therapy and colorectal cancer: an update.
J Br Menopause Soc
2006
;
12
:
139
–42.
12
Newcomb PA, Storer BE. Postmenopausal hormone use and risk of large-bowel cancer.
J Natl Cancer Inst
1995
;
87
:
1067
–71. [Erratum, J Natl Cancer Inst 1995;87:1416.]
13
Newcomb PA, Zheng Y, Chia VM, et al. Estrogen plus progestin use, microsatellite instability and the risk of colorectal cancer in women.
Cancer Res
2007
;
67
:
7534
–9.
14
Herbert-Croteau N. A meta-analysis of hormone replacement therapy and colon cancer in women.
Cancer Epidemiol Biomarkers Prev
1998
;
7
:
653
–9.
15
Chan JA, Meyerhardt JA, Chan AT, Giovannucci EL, Colditz GA, Fuchs CS. Hormone replacement therapy and survival after colorectal cancer diagnosis.
J Clin Oncol
2006
;
24
:
5680
–6.
16
Slattery MT, Ballard-Barbash R, Edwards S, Caan BJ, Potter JD. Body mass index and colon cancer: an evaluation of the modifying effects of estrogen.
Cancer Causes and Control
2003
;
14
:
75
–84.
17
The WHI Steering Committee. Effects of conjugated equine estrogens in postmenopausal women with hysterectomy: the Women's Health Initiative randomized controlled trial.
JAMA
2004
;
291
:
1701
–12.
18
The Women's Health Initiative Study Group. Design of the Women's Health Initiative clinical trial and observational study.
Control Clin Trials
1998
;
19
:
61
–103.
19
Mandelson MT, Miglioretti D, Newcomb PA, Harrison R, Potter JD. Hormone replacement therapy in relation to survival in women diagnosed with colon cancer.
Cancer Causes and Control
2003
;
14
:
979
–84.
20
National Cancer Institute. About SEER. Available at http://www.seer.cancer.gov/. Accessibility verified March 28, 2005.
21
Hulley S, Furgerg C, Barrett-Connor E, et al. Noncardiovascular disease outcomes during 6.8 years of hormone therapy. Heart and Estrogen/Progestin Replacement Study Follow-up (HERS II).
JAMA
2002
;
288
:
58
–66.
22
Stefanick ML, Hsai J, Barad D, Johnson SJ, Cochrane B, Liu J. The Women's Health Initiative postmenopausal hormone trials: overview and baseline characteristics of participants.
Annals Epidemiol
2003
;
13
:
S78
–86.
23
Janne PA, Mayer R. Chemoprevention of colorectal cancer.
N Engl J Med
2000
;
342
:
1960
–8.
24
Grodstein F, Newcomb PA, Stampfer MJ. Postmenopausal hormone therapy and the risk of colorectal cancer: a review and meta-analysis.
Am J Med
1999
;
106
:
574
–82.
25
Calle EE, Miracle-McMahill HL, Thun MJ, Heath CW, Jr. Estrogen replacement therapy and risk of fatal colon cancer in a prospective cohort of postmenopausal women.
J Natl Cancer Inst
1995
;
87
:
517
–23.
26
Campbell PT, Newcomb P, Gallinger S, Cotterchio M, McLaughlin JR. Exogenous hormones and colorectal cancer risk in Canada: associations stratified by clinically defined familial risk of cancer.
Cancer Causes Control
2007
;
18
:
723
–33.
27
Persson I, Yuen J, Bergkvist L, Schairer C. Cancer incidence and mortality in women receiving estrogen and estrogen-progestin replacement therapy—long-term follow-up of a Swedish cohort.
Int J Cancer
1996
;
67
:
327
–32.
28
Tannen RL, Weiner MG, Xie D, Barnhart K. Estrogen affects postmenopausal women differently than estrogen plus progestin replacement therapy. Hum Reprod 2007;March 8 [Epub ahead of print].
29
Slattery ML, Anderson K, Sanowitz W, et al. Hormone replacement therapy and improved survival among postmenopausal women diagnosed with colon cancer (USA).
Cancer Causes Control
1999
;
10
:
467
–73.
30
The Writing Group for the PEPI Trial. Effects of hormone replacement therapy on endometrial histology in postmenopausal women. The Postmenopausal Estrogen/Progestin Interventions (PEPI) trial.
JAMA
1996
;
275
:
370
–5.
31
Chlebowski RT, Hendrix SL, Langer RD, et al. Influence of estrogen plus progestin on breast cancer and mammography in healthy postmenopausal women: the Women's Health Initiative randomized trial.
JAMA
2003
;
289
:
3243
–53.
32
Stefanick M, Anderson GL, Margolis KL, et al. Effects of conjugated equine estrogens on breast cancer and mammography in postmenopausal women with hysterectomy: the Women's Health Initiative randomized trial.
JAMA
2006
;
295
:
1647
–57.
33
Rabeneck L, Davila J, Thompson M, El-Serag. Outcomes in elderly patients following surgery for colorectal cancer in the Veterans Affairs health care system.
Al Ther
2004
;
20
:
1115
–24.
34
Prihartono N, Palmer JR, Louik C, Shapiro S, Rosenberg L. A case-control study of use of postmenopausal female hormone supplements in relation to the risk of large bowel cancer.
Cancer Epidemiol Biomarkers Prev
2000
;
9
:
443
–7.
35
Pischon T, Lahmann PH, Boeing H, et al. Body size and risk of colon and rectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC).
J Natl Cancer Inst
2006
;
98
:
920
–31.
36
Wang Y, Jacobs EJ, Teras LR, et al. Lack of evidence for effect modification by estrogen of association between body mass index and colorectal cancer risk among postmenopausal women.
Cancer Causes Control
2007
;
18
:
793
–9.
37
Hoffmeister M, Raum E, Winter J, Chang-Claude J, Brenner H. Hormone replacement therapy, body mass, and the risk of colorectal cancer among postmenopausal women from Germany.
Br J Cancer
2007
;
97
:
1486
–92.
38
Lin J, Zhang SM, Cook NR, Rexrode KM, Lee IM, Buring JE. Body mass index and risk of colorectal cancer in women (United States).
Cancer Causes Control
2004
;
15
:
581
–9.
39
Saydeh SH, Platz EA, Rifai N, Pollak MN, Brancati FL, Helzlsouer KJ. Association of markers of insulin and glucose control with subsequent colorectal cancer risk.
Cancer Epidemiol Biomarkers Prev
2003
;
12
:
412
–8.
40
Thomas ML, Xu X, Norfleet AM, Watson CS. The presence of functional estrogen receptors in intestinal epithelial cells.
Endocrinology
1993
;
132
:
426
–30.
41
Witte D, Chirala M, Younes A, Li Y, Younes M. Estrogen receptor beta is expressed in human colorectal adenocarcinoma.
Hum Pathol
2001
;
32
:
940
–4.