ABSTRACT
The hormone dependency of rat mammary tumor model has been demonstrated by a regression of the tumor in response to ovariectomy or hypophyscctomy, and by the presence of estrogen receptors in the tumor tissue. The tumor gradually loses its hormone responsiveness. The tumors were removed, cut into small pieces, and transplanted into syngeneic female recipients of 90 days old. Tumors, serially transplanted into intact recipients, are able to grow to 1.5 to 2.0 cm in diameter within I to 2 months. Rat mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) are often used as an experimental model for hormone-dependent tumors. DMBA-induced mammary tumors in rats can gradually lose their hormone dependency and finally become hormone independent by serial transplantation into syngeneic hosts. In addition to the experimental model for studying hormone dependency, the presence of morphologically and functionally distinct cell types in DMBA-induced mammary tumors offers an excellent experimental system for studying cell selection.
