Endocrine-dependent rat mammary tumor regression: use of a gonadotropin releasing hormone analog.

Long-term administration of [D-Leu6, des-Gly-NH210, Pro-ethylamide9]-GnRH, an analog of gonadotropin releasing hormone, caused regression of neoplastic tissue in a rat bearing a spontaneous mammary adenocarcinoma and in rats in which tumors had been induced by treatment with dimethylbenzanthracene (DMBA). During two separate treatment periods with the analog, the tumor in the single animal regressed although it had previously grown spontaneously. After a third period of growth, ovariectomy also induced regression, suggesting endocrine dependency of the tumor. These observations were confirmed in the DMBA-induced tumor system, where tumor regression in the analog-treated rats was comparable to that observed in the ovariectomized rats, and in both cases the tumor regression was significant when compared to untreated controls.