Diazepam use and progression of breast cancer.

The relationship between diazepam and breast cancer was evaluated using data from a case-control study of breast cancer, in which 1075 cases and 1146 controls who were participants in a breast cancer screening program were interviewed. Diazepam use was negatively associated with extent of disease and lymph node involvement, and this effect seemed greatest for long-term users of diazepam. It is not certain to what extent these data reflect an ascertainment bias, an association with the reasons for which the drug was prescribed, or chance. Whatever the explanation, the findings do not support a previous contention that diazepam promotes or accelerates breast cancer growth.