Radiogenic neoplasia in thyroid and mammary clonogens. Final progress report, 1 January 1987--31 December 1997

The induction of cancer by ionizing radiation is a matter of great practical importance to the nuclear industry, to national defense, to radiological medicine and to the general public. It is increasingly apparent that carcinogenesis is a leading dose-limiting effect of radiation exposure. The thyroid and mammary glands are among the most sensitive human tissues to radiogenic initiation of cancer, and there is a profoundly higher risk of neoplastic initiation in these glands among individuals irradiated before or during puberty than among those exposed in later life. The authors developed unique quantitative experimental models to investigate and characterize the cells of origin of thyroid and mammary cancers and the effects of radiation on them (C185). To study these progenitor cells in vivo it is necessary to have a system by which their concentrations, total numbers and responses to radiation and other factors can be measured. It is a truism that not all cells in a tissue are equally sensitive to neoplastic initiation. They reasoned that the progenitor cells are most likely members of that subpopulation that is necessary to maintenance of normal tissue cell numbers and to repair and replacement after tissue damage. They further reasoned that such cells would likely be responsive to specific mitogenic stimulation by hormones. On the basis of these considerations, they developed quantitative rat thyroid and mammary epithelial cell transplantation systems