Nonsteroidal anti-inflammatory drug use and breast cancer risk.

Findings from previous epidemiological studies are inconclusive, though they suggest nonsteroidal anti-inflammatory drug (NSAID) use is associated with a reduction in breast cancer risk. In addition, animal studies report that NSAIDs inhibit mammary tumor development. The association between NSAID use and breast cancer risk was evaluated using a case-control study design. Cases were a random sample of women diagnosed with a first primary cancer of the breast, aged 25-74 years, identified through the Ontario Cancer Registry, and diagnosed between July 1996 and September 1998. Controls were an age-matched random sample of the female population of Ontario. Cases (n = 3133) and controls (n = 3062) completed a mailed questionnaire with information on their past use of NSAID and other medications, as well as many risk factors thought to be associated with breast cancer. Multivariate logistic regression analysis was used to obtain adjusted odds ratio (OR) estimates. Use of any NSAID medication (daily use for > or =2 months) was found to be associated with a significant 24% reduction in breast cancer risk (OR = 0.76; 95% confidence interval: 0.66, 0.88). The reduced risk was strongest for use lasting > 8 years, compared with nonusers (OR = 0.68; 95% confidence interval: 0.54, 0.86). No marked trends were observed for time since first use or last use or age at first use. Our results suggest a reduction in breast cancer risk associated with any regular NSAID use. NSAID use is a modifiable factor, and any protective effect attributed to its use could be of great public health importance.