Effects of serial passage on the endocrine response and steroid metabolism of a rat mammary carcinoma.

A rat mammary carcinoma induced by 7-12 dimethylbenzanthracene was serially transplanted into successive generations of thymectomized host animals. After its 2nd passage, the growth of the tumour appeared hormone-dependent, regressing after oophorectomy and regrowing with administration of oestradiol 17 beta to the host. Third-generation transplanted tumours, however, showed only a transient regression after oophorectomy, and the growth of tumours after further passages appeared ovary-independent. Loss in hormone dependency was not accompanied by histological changes. There was however a progressive increase with successive transplantation in the ability of tumours to metabolize 7 alpha [3H] testosterone in vitro. This was accounted for by raised conversion to 5 alpha androstanediol.