Alteration of the effects of cancer therapy agents on breast cancer cells by the herbal medicine black cohosh.

Recent studies have revealed that many, perhaps most, patients receiving cancer therapy are simultaneously self-medicating with one or several complementary and alternative medicines, often without discussing the use of these agents with their physicians. The effects of these agents on the efficacy and toxicity of standard anticancer therapy have not been studied. The experiments described in this report used a well characterized mouse breast cancer cell line to ask whether commercially available extracts of black cohosh, an herb widely used by breast cancer patients, altered the response of cancer cells to radiation and to four drugs commonly used in cancer therapy. The black cohosh extracts increased the cytotoxicity of doxorubicin and docetaxel and decreased the cytotoxicity of cisplatin, but did not alter the effects of radiation or 4-hydroperoxycyclophosphamide (4-HC), an analog of cyclophosphamide which is active in cell culture. These data sound a warning that the herbal medicines being used by patients undergoing cancer therapy can have effects on cancer cells that alter their response to the agents commonly used to treat breast cancer.