3H-thymidine incorporation into mammary carcinoma cells obtained by needle aspiration before and during endocrine therapy.

3H-thymidine autoradiography was used to evaluate DNA-synthesis in carcinoma cells obtained by fine-needle aspiration biopsy from mammary carcinomas. Needle aspirates were analyzed before and after oophorectomy, and before and during treatment with oestrogen or anti-oestrogen (tamoxifen). Tumor regression occurred in 18 patients-in one of four following oophorectomy, in 15 of 38 treated with tamoxifen and in two of three given oestrogen. Seven tumors remained stationary for long periods-up to a year. In 20 cases there was tumor progression. Regression of tumors was preceded by a decrease in the fraction of 3H-thymidine-labeled cells (s-phase cells). The tumors that remained stationary or progressed retained significant levels of 3H-thymidine incorporation. This study thus showed that 3H-thymidine autoradiography can give an early estimate of tumour response to endocrine therapy. Considerable differences were found between the carcinomas in regard to proportions of S-phase cells. Further insight into this parameter may be useful for planning chemotherapy with S-phase specific agents.