Cimetidine use and risk of breast, prostate, and other cancers

Purpose - The study was conducted to examine whether use of cimetidine is a ssociated with the risk of cancer, with special attention to cancers of the breast and prostate because cimetidine increases estradiol levels and inte rferes with androgen binding. Methods - Individuals who received a prescription of cimetidine were identi fied from two computerized pharmacy databases of medications dispensed at N orthern California Kaiser Permanente between 1982 and 1987. Users of raniti dine, a histamine-2 receptor antagonist that does not appear to influence e strogen levels or androgen binding, and non-users of either cimetidine or r anitidine, were also identified from these databases. Study subjects were f ollowed through December 1995 for new diagnoses of cancer. Cox regression w as used to estimate relative risks of cancer associated with use of cimetid ine and ranitidine. Non-users of cimetidine and ranitidine were the referen t group for all analyses. Results - While there were very modest increases and decreases in risk for some cancer sites among cimetidine users, most were within the limits of ch ance given no true association. Furthermore, similar risks of these cancers were also observed among ranitidine users. Conclusions - Although our results do not support an association between ca ncer risk and cimetidine use, it is one of the most widely prescribed drugs in the US and may now be purchased over-the-counter. The potential effect of cimetidine on risk of cancer, especially those that are hormone-related, should continue to be monitored, preferably in larger study populations. C opyright (C) 2000 John Wiley & Sons, Ltd.