Objective: Cimetidine, a histamine2-receptor antagonist (H 2 blocker) commonly used to treat symptoms of peptic and duodenal ulcer, influences both hormonal and immune pathways. We investigated the influence of cimetidine use on the risk of breast cancer in our hospital-based case control surveillance study. Methods: Data on medication use and other factors were elicited from patients admitted to hospitals from 1977 to 2002. We compared 6,994 breast cancer cases with a control group comprising cancer (n = 2,478) and noncancer (n = 6,004) diagnoses. Conditional logistic regression models were used to estimate odds ratios for H2 blocker use that began at least 1 year prior to admission. Regular use was defined as use for at least 4 days per week for at least 3 continuous months. Results: The odds ratio for breast cancer among regular users of cimetidine was 0.9 (95% confidence interval, 0.6-1.2) using a combined cancer and noncancer control group. For use of 4 or more years' duration, the odds ratio was <1.0 but was not statistically significant. The odds ratio for the regular use of other H 2 blockers was 0.9 (95% confidence interval, 0.6-1.3). Conclusions: Our data agree with data from three prior studies which indicate that cimetidine is not associated with the risk of breast cancer. Other H2 blockers were also unrelated to the risk of breast cancer.
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