Sequential assays of hormone receptors and the Tritiated Thymidine Labeling Index in 7,12-dimethylbenz(a)anthracene-induced rat mammary cancers.

This study was carried out to determine whether hormone receptors and the Tritiated Thymidine Labeling Index (TLI) would change with intervening treatment in 7,12-dimethylbenz(a)anthracen-induced rat mammary cancer as well as to evaluate their predictive significance. Forty-eight tumors were studied. TLI significantly correlated inversely with the binding sites of cytoplasmic estrogen receptors (ERC), but not of cytoplasmic progesterone receptors (PRC). From the response to the two treatments ovariectomy or adriamycin, it was demonstrated that ERC was a predictor of the response to ovariectomy and TLI showed a predictive value in the response to adriamycin. Ovariectomy generally induced a marked decrease in ERC level and PRC level, whereas adriamycin led to an increase and decrease in ERC level and PRC level, respectively. TLI showed a remarkable decrease in tumors which were responsive to ovariectomy or adriamycin. Some tumors, which had been the intermediate or ineffective group with a previously given treatment, were evaluated for the first time as being the effective group with another type of treatment. These results suggest that the response to treatment for breast cancer may change over the clinical course and ideal treatment for advanced breast cancer should included concomitant chemo-endocrine therapy.