Obesity may increase the risk of breast cancer and decrease survival in postmenopausal women through higher levels of circulating estrogen. The mortality risk is greater in younger women, but studies of women ≥ 65 years are limited. Consenting women ≥ 65 years at incident diagnosis of stage I (tumor ≥ 1 cm), stage II, or stage IIIA primary breast cancer from Los Angeles, Minnesota, North Carolina, or Rhode Island were interviewed by telephone 3 months (baseline) after their definitive surgery (N=658) and were followed annually for 9 years unless death, loss to follow‐up, or refusal to continue participation occurred. BMI was calculated using weight (kilograms [kg]) and height (meters [m]) reported at baseline (BMI 25–29 kg/m2 = overweight; BMI ≥ 30 kg/m2 = obese). Women with a healthy BMI (< 25 kg/m2) comprised the reference group. Recurrence was collected during follow‐up interviews. Death was confirmed by a Social Security Death Index search through March 2009 and date and cause of death were collected from the National Death Index through 2004. Demographic characteristics (age, race, marital status, education, geographic location, and Charlson Comorbidity Index [CCI]) were collected at baseline. Breast cancer tumor (stage, histologic grade, estrogen receptor expression) and treatment (primary therapy, adjuvant chemotherapy receipt, adjuvant tamoxifen receipt) characteristics were collected from medical records. Of our cohort, 34% were overweight and 21% were obese (mean BMI, 25.7 kg/m2). The majority of overweight women were 70–74 years old (29%), had a CCI of 0 (62%), and completed college or higher (53%); obese women were mostly 65–69 years (34%), had a CCI of 2 (13%) and only completed up to high school (40%). Women who were overweight (Odds Ratio [OR]=1.5; 95% Confidence Interval [CI]=0.8, 2.7) or obese (OR=1.6; 95% CI=0.8, 3.1) had an increased the risk of recurrence compared with women with a healthy BMI. Being overweight was not associated with breast cancer‐specific mortality or allcause mortality. Obese women had nearly a twofold increased risk of dying from breast cancer (OR=1.9; 95%CI=0.7, 5.0); obesity was weakly associated with the risk of dying from any cause (OR=1.2; 95%CI=0.7, 1.8). Weight at baseline and 6 years later were consistently reported by the women in our study. Since women do not tend to overestimate their weight, our results conservatively estimate the effect of obesity on breast cancer outcomes. Unlike many previous studies, we had detailed information regarding primary and adjuvant treatment, which are important in estimating the risk of breast cancer recurrence and mortality. Although our data are compatible with a 20–30% decreased risk of breast cancer outcomes, our findings suggest higher body mass after breast cancer diagnosis is associated with negative outcomes in older women. Achieving or maintaining a healthy BMI after definitive surgery may improve breast cancer prognosis.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):PR-08.