Nonsteroidal Anti-Inflammatory Drugs and Prostate Cancer Risk in the VITamins And Lifestyle (VITAL) Cohort Free

There is increasing evidence which suggests that chronic inflammation is important in prostate carcinogenesis (1, 2). Prostatitis has been associated with prostate cancer risk and proliferative inflammatory atrophy of the prostate, a condition marked by chronic inflammation, may be an early precursor lesion for prostate cancer (1, 2). Nonsteroidal anti-inflammatory drugs (NSAIDs) have anticancer properties in vitro and in vivo (3, 4), in support of epidemiologic studies that have shown reductions in prostate cancer risk for aspirin use in particular (5). Many epidemiologic studies of NSAID use and prostate cancer risk, however, are limited by short-term measurement of NSAID use and most do not adjust for indications of use.

Here we examine the association of long-term NSAID use with prostate cancer risk in the VITamins And Lifestyle (VITAL) cohort study.

Participants were male members of the VITAL cohort (6). Men, age 50–76 years, living in the region of Washington State covered by the Surveillance, Epidemiology, and End Results (SEER) cancer registry, were eligible to participate. Between October 2000 and November 2002, we mailed baseline questionnaires to 195,465 men. Of these, 37,382 (19.1%) were returned and deemed eligible for inclusion in the VITAL cohort. For this analysis, exclusions were made for men who: had a history of prostate cancer (n = 2,013), were missing key variables (cancer history at baseline or NSAID use [n = 1,235]), or had a subsequent diagnosis of incident in situ prostate cancer (n = 2), leaving, 34,132 available for analysis.

Participants completed a baseline questionnaire that included questions on regular use (≥1 day/week for ≥1 year) of NSAIDs, including frequency and years of use in the past 10 of low-dose aspirin, regular or extra-strength aspirin, ibuprofen, naproxen, and celecoxib/rofecoxib. Ten-year average use of each drug was categorized into nonuser; low use, <4 days/week or <4 years; and high use, ≥4 days/week and ≥4 years. Participants also reported on known or suspected risk factors for prostate cancer as well as health conditions that are possible indications of NSAID use.

Participants were followed for incident prostate cancer diagnoses via linkage to the SEER registry. Between baseline and December 31, 2007, there were 1,550 incident prostate cancer cases diagnosed. High-grade tumors were defined as Gleason scores 8–10 and 7 (4 + 3). Low-grade tumors were Gleason scores 2–6 or 7 (3 + 4). As primary and secondary Gleason scores were not available from SEER for prostate cancers diagnosed prior to 2004, analyses by grade were restricted to incidence data from 2004–2007 only (733 low-grade and 213 high-grade).

We estimated hazard ratios (HR) and 95% confidence intervals (95% CI) for total prostate cancer and prostate cancer by grade in relation to NSAID use with Cox proportional hazards regression models, using participants' age as the time metric. Prostate cancer risk factors as well as potential indications for NSAID use were identified a priori for adjustment in multivariable models (see footnote b of Table 1). P-values for trend were calculated by treating categorical variables as ordinal in the models. We calculated minimum detectable risks (MDR) given 80% power (7). For comparisons of use to nonuse of each NSAID, we had an MDR of 0.85; for comparisons of high 10-year average use to nonuse, the MDR was 0.80 for low-dose and regular strength aspirin, 0.69 for ibuprofen, and 0.73 for nonaspirin NSAIDs.

Use of NSAIDs was not associated with total prostate cancer risk (Table 1). When the analysis was stratified by prostate cancer grade (Table 2), use of regular-strength aspirin was suggestive of an inverse association with high- (HR 0.73, 95% CI: 0.53–1.02) but not low-grade (HR 1.04, 95% CI: 0.89–1.23) prostate cancer. No differences were observed for the remaining NSAIDs by grade or by stage (local vs. regional/distant; data not shown).

We observed no association of use of individual NSAIDs with total prostate cancer risk in this cohort. In contrast to our findings, 2 recent meta-analyses reported 11% (HR 0.89, 95% CI: 0.77–1.03) (8) and 17% (HR 0.83, 95% CI: 0.76–0.91) (5) reductions in total prostate cancer risk among 6 and 9 prospective studies of aspirin use, respectively. It may be that the null result we observed with aspirin use and total prostate cancer risk is due to residual confounding by PSA testing, as we only collected data on PSA testing at baseline. If aspirin use is positively associated with subsequent prostate cancer screening, a small reduction in risk would be negatively confounded toward 1.0.

One meta-analysis reported on the association of NSAID use with advanced prostate cancer; in it aspirin use was associated with a 17% (HR 0.83, 95% CI: 0.73–0.95) reduction in risk among 6 prospective studies (5). Our finding of a 27% statistically nonsignificant lower risk of high-grade prostate cancer among users of regular–strength aspirin is consistent with this estimate (5). In support of our findings, the meta-analyses did not find a reduction in risk of total (5, 8) or advanced (5) prostate cancer among prospective studies of nonaspirin NSAIDs.

The advantages of this study include its assessment of NSAID use over a 10-year period prior to baseline, and the separate assessment of use of low-dose aspirin, regular dose aspirin, ibuprofen, naproxen, and COX-2 inhibitors. We were also able to control for confounding by multiple indications for NSAID use. Nonetheless, these differences do not explain the discrepancies between our findings and those of other published reports.

In summary, our findings do not support an association of NSAID use with prostate cancer risk, but do provide limited support for a reduction in high-grade prostate cancer with aspirin use.

No potential conflicts of interest were disclosed.

This work is supported by grants R25-CA94880 and K05-CA154337 from the National Institutes of Health, National Cancer Institute.