[Choice of second-line chemotherapy for advanced breast cancer based on the chemosensitivity assay by in vitro colony assay].

The efficacy of anticancer drugs and the development of drug resistance after chemotherapy for advanced breast cancer has been evaluated in vitro using the human tumor clonogenic assay (in vitro colony assay technique.) The rates of in vitro chemosensitivity to various anticancer drugs in untreated patients were similar or somewhat higher than the clinical efficacy reported for single clinical use of the drugs. The results of in vitro chemosensitivities to the drugs against previously treated patients showed decreased chemosensitivities to the drugs which had been used, especially adriamycin and mitomycin C. In contrast to this, in vitro chemosensitivities to 5-FU, methotrexate and L-PAM were unchanged after exposure to combination chemotherapy consisting of these drugs. This result suggests that the development of resistance to these drugs is minimal at the doses used in our protocol. The overall chemosensitivity rate for anthracyclines including adriamycin in vitro was only 5% (5/93) for previously treated patients, compared with 41% (35/83) for vinca alkaloids (p less than 0.005). This finding indicates that combination chemotherapy including vinca alkaloids is the appropriate selection for second line chemotherapy for advanced breast cancer patients who have been treated previously with adriamycin.