Evidence Against a Direct Carcinogenic Effect of X-Rays In Vitro

Abstract

The carcinogenic effect of a single 300-rad dose of X-rays on cells of nonmalignant established mouse cell lines was investigated. Malignant transformation was induced in some lines under certain conditions; e.g., low viability, high cell concentration resulting in close contact between viable and nonviable cells, and cell debris. The same amount of cell damage caused by the radiation was mechanically induced and resulted in a comparable incidence of malignant transformation. This supports the hypothesis that the carcinogenic effect of irradiation on cells is related to the presence of dead and damaged cells in close contact with viable cells; it argues against a direct carcinogenic effect of radiation on cells.