Cancer occurrence in a cohort of patients treated with cimetidine.

The possible carcinogenic effects of antisecretory agents used in the treatment of gastric and duodenal ulcer were investigated in a population based cohort study of 16,739 patients who were prescribed the H2-antagonist cimetidine between 1977 and 1981. An excess risk for gastric cancer was observed, with a relative risk of about 10 in the first year after beginning use of the drug, which decreased thereafter. A similar pattern was seen for cancers of the colon, pancreas and gall bladder, and for non-Hodgkin's lymphoma. These increased risks probably represent cases in which a malignancy was misdiagnosed as a gastric ulcer. The excess risk for gastric cancer was unaffected by the method of diagnosis, the risk in those who had undergone an endoscopy being similar to those who had been diagnosed by an x-ray examination. A relative risk of 1.5-2.0 was observed for cancer of the respiratory organs, with no effect of latency, indicating that there are common risk factors for peptic ulcer and for lung cancer. Although the observed increases in cancer risk in persons receiving cimetidine is probably caused by factors other than a carcinogenic action of the drug itself, this possibility cannot be ruled out because of the short period of follow up.