Cimetidine use and risk of prostate and breast cancer

Histamine (H-2) receptor antagonists, such as cimetidine and ranitidine, be came available in the late 1970s and presently number among the most common ly used drugs. Cimetidine has been hypothesized to exert a cancer preventiv e effect on the prostate due to its ability to inhibit the binding of dihyd rotestosterone to androgen receptors. Other hormonal effects of this drug i nclude increases in serum prolactin levels and inhibition of 2-hydroxylatio n of estradiol. We assessed risk of prostate and breast cancers in a cohort of 48,512 members of the Group Health Cooperative of Puget Sound prescribe d cimetidine or another H-2 blocker between 1977 and 1995. Standardized inc idence ratios were calculated comparing the observed numbers of cancers to those expected based on population rates in western Washington State. Becau se cimetidine, but not other H-2 blockers, influences hormonal activity and metabolism, we conducted nested case-control studies comparing cancer risk among individuals treated with cimetidine to individuals who used other H- 2 blockers. Risks of breast and prostate cancers were identical among users of cimetidine and users of other H-2 blockers (relative risk, 1.0 for both cancers). We observed no trend in risk of breast cancer according to time since first or last cimetidine prescription or number of cimetidine prescri ptions filled. For prostate cancer, our findings were similar save for a mo dest increase in risk among men who had filled greater than or equal to 21 cimetidine prescriptions (relative risk, 1.4; 95% confidence interval, 1.0- 1.9). Our results suggest that use of cimetidine does not influence risk of female breast cancer. Further, these data provide little evidence to suppo rt the previously hypothesized preventive effect of cimetidine on risk of p rostate cancer.