Nonhormonal drugs and cancer.

Nonhormonal drugs probably account for only a small proportion of human cancer but have contributed many valuable insights into carcinogenic mechanisms. The antineoplastics, radiopharmaceuticals, and a few other agents account for most of the known drug-induced cancer. A number of other agents are under suspicion, usually due to studies in laboratory animals or to preliminary clinical or epidemiologic observations. This group includes some drugs in widespread use such as clofibrate and cimetidine. For a few drugs that are carcinogenic in animals, such as dapsone and isoniazid, epidemiologic studies have shown little to no evidence of carcinogenicity. Recent experimental studies have shown tumor promotion by the commonly used antidepressants amitriptyline and fluoxetine and some antihistamines, which deserve epidemiologic investigation of cancer risk. Some drugs may also protect against cancer, as suggested by the lower risk of colorectal cancer among regular users of nonsteroidal antiinflammatory drugs. Pharmacoepidemiologic studies must take into account possible confounding by the original conditions for which drugs were taken and the typically long latency period of drug-induced cancer. Improved postmarketing surveillance, continued routine case-control surveillance, and ad hoc case-control and cohort studies are needed to evaluate drugs already in use as well as newly introduced agents.