Selective effects of insulin and hydrocortisone on colony formation and chemosensitivity of human tumors in soft agar

Because low plating efficiencies of most human cancers severely limit the number of successful chemosensitivity tests that can be performed, we studied the growth‐enhancing effects of insulin and hydrocortisone on a variety of solid tumors. Colony formation in soft agar was significantly increased in 23/49 (47%) tumors treated with 3 U/ml insulin, whereas fewer colonies were observed in 7 (14%). These effects were highly selective for tumor type. Colony growth for ovarian, lung, and colon carcinomas increased by 123%, 37% and 28%, respectively. In contrast, insulin inhibited the growth of melanoma, kidney, and breast tumors. Hydrocortisone at 0.05 μg/ml increased colony numbers in 23/45 (51%) tumors, while in 7 (16%) colony numbers were decreased. Growth of ovarian, lung, breast, and kidney carcinomas was increased by 136%, 126%, 78% and 69%, respectively, whereas melanomas, sarcomas, and colon tumors were inhibited by hydrocortisone. In vitro chemosensitivities were relatively unchanged by the hormones. In 168 (134 paired) drug/tumor tests, sensitivity to standard antineoplastic drugs in the presence or absence of hormones was concordant 82% of the time (correlation coefficient, 0.71). However, in 20 tests (15%), significant enhancement of chemosensitivity was observed. We concluded that cloning efficiencies of many common human tumor types can be improved with hormones, and that these growth‐enhancing effects are selective for tumor type.