Thyroid hormone modulation of X ray-induced in vitro neoplastic transformation

The direct oncogenic potential of X rays has been demonstrated by the in vitro neoplastic transformation of mammalian cells in culture, a technique which permits the study of oncogenesis in the absence of host-specific effects. Although several agents are known to modulate in vitro neoplastic transformation by X rays, little is known of the effects of hormones. We now describe experiments which show that the presence of thyroid hormone is necessary for in vitro neoplastic transformation by X rays in cells of an established mouse fibroblast culture (C3H/10T1/2) and in early-passage diploid hamster embryo cells.