Diazepam and the risk of breast cancer.

The relation of breast cancer to diazepam use was evaluated in a case-control study of 1236 women with breast cancer and 728 control subjects with other malignancies. Compared to women who never used diazepam, the relative risk for women who used the drug at least 4 days per week for at least 6 months was estimated to be 0.9, with 95% confidence limits of 0.5 and 1.6. There was no apparent association for recent use, or for use in the distant past, although confidence intervals were fairly wide in these categories. The results were not explained by various potential confounding factors, including the major risk factors for breast cancer. The findings suggest that regular diazepam use does not increase the risk of breast cancer relative to other cancers.