[Experimental studies on the enhanced effects of chemoendocrine therapy in breast cancer]

The clinical response rate of chemotherapy or endocrine therapy for advanced or recurrent breast cancer has been described as being about 30%, regardless of steroid hormone status. However, the response rate for endocrine therapy is about double in patients with positive estrogen receptor. In order to obtain a higher response rate than that for single therapy, experimental attempts were made to combine cytotoxic agents, antiestrogenic agents, ablative therapy and immunotherapy from the viewpoints of tumor cell kinetics, natural killer activity and interferon activity of spleen cells. Tamoxifen and orchiectomy were shown by flow cytometry to produce a G1 block, increasing the G0, G1 phase and decreasing the S phase, in MCF-7 cells in vitro and in SC 115 cells, in vivo respectively, for a long period. On the other hand, 5-FU showed most effective cytotoxicity in the S phase of both types of tumor cells in vitro and in vivo, although the depressed S phase recovered within 24 hours. Therefore, any combined chemo-endocrine therapy should be devised so that the endocrine therapy maintains a G1 block for a long period and performed immediately following chemotherapy during the decreased S phase of the tumor cells. N K activity of spleen cells were enhanced, and interferon production in spleen cells was not changed by ovariectomy in C3H/He mice compared with sham-operated mice. It is suggested that endocrine therapy may affect the immunopotentiality of cancer patients.