In vitro radiation response of cells from four human tumors propagated in immune-suppressed mice.

Two recently developed clonogenic assays for human tumor cells have been used to measure the in vitro radiation cell survival of four human tumors, a pancreatic carcinoma, a colonic carcinoma, an oat cell carcinoma of the lung, and a melanoma, propagated as xenografts in immune-suppressed mice. The slopes and shoulders of the survival curves for the first three tumors were all similar with Do's, respectively, of 94, 100, and 131 rads and with Dq's, respectively, of 8, 44, and 41 rads, However, melanoma cells from the fourth tumor had a survival curve that differed from those of the other three, both in having a wider shoulder with a Dq of 216 rads and in having a shallower slope with a Do value of 183 rads. It is suggested that the wide shoulder to the melanoma cell survival curve may in part explain the poor response to small fractionated doses of radiotherapy usually observed clinically for this tumor type. However, the data from the other three tumors suggest that differences in radiotherapeutic response seen in the clinic for these tumors cannot be attributed to differences in intrinsic radiosensitivity of the tumor cells.