Low dose rate ionizing radiation induces increased growth capacities of d-deletion retinoblastoma skin fibroblasts.

Skin fibroblasts from normal children and three children with a 13q deletion retinoblastoma (Rb) were exposed to cumulative low doses of gamma rays. The typical response of normal donors was a reduction in the lifespan of irradiated fibroblasts, the precocity of the decline being inversely related to the dose received. In contrast, the lifespan of one Rb cell line (Rb1) was prolonged; irradiated cells with an increased growth potential showed a higher number of cells at confluency and more cells were entering DNA synthesis phase than in non-irradiated cells. Another Rb cell line (Rb2) demonstrated a normal lifespan following irradiation but foci were observed in irradiated cultures. Cytogenetic analysis revealed no selection of abnormal clones in these cell populations. The third Rb line examined (Rb3) responded like a normal cell line. We suggest that irradiated skin fibroblasts derived from some patients with Rb are in certain cases able to express abnormal growth capacities which may be one of the manifestations of the high susceptibility of the individual's stromal cells to carcinogenic agents.