In vitro evaluation of anticancer drugs in relation to development of drug resistance in the human tumor clonogenic assay.

The efficacy of anticancer drugs against ovarian cancer, breast cancer, and colorectal cancer has been evaluated in vitro by the human tumor clonogenic assay developed by Hamburger and Salmon. The in vitro colony assay method used in this study is a minor modification of their method and was used in 83 patients with ovarian cancer, 47 patients with breast cancer, and 13 patients with colorectal cancer. The total numbers of assays performed in vitro were 258 for ovarian cancer, 87 for breast cancer, and 38 for colorectal cancer. The average chemosensitivity rates to single agents tested were 35% and 32% in the untreated patients with ovarian and breast cancer, respectively. In contrast to this result, the chemosensitivity rate of the untreated patients with colorectal cancer was only 16%. Consisting the clinical efficacy of anticancer drugs against these tumors, these results suggest that there is a correlation between chemosensitivity in the human tumor clonogenic assay and clinical responsiveness. In this assay the chemosensitivity in specimens from ovarian cancer patients who had had prior chemotherapy was significantly lower than in those from nonpretreated patients (P less than 0.05). This seems to indicate the development of drug resistance after treatment with anticancer drugs. These results suggest that the human tumor clonogenic assay is a useful tool for the evaluation of antitumor effects of drugs in vitro.