[Chemo- and endocrino-therapy of breast carcinoma xenografts in the dormant or exponential growth phase].

In case of concerning about recurrence case after operative treatment of breast cancer, we must suppose existence of dormant breast cancer cell. To elucidate a rational treatment of the breast cancer in the dormant stage, we have developed a new treatment model using human breast carcinoma xenografts (MCF-7, R-27 and Br-10) in nude mice. After the sc inoculation of the tumors, the treatment was initiated with or without the previous estradiol (E2) stimulation. While MCF-7 was sensitive to mitomycin C (6 mg/kg i.p.) and and tamoxifen pellet (2.5 mg/mouse s.c.) in the dormant and exponential growth phase, R-27 and Br-10 were sensitive to the drugs only in the exponential growth phase but not in the dormant stage. These results suggested that the sensitivity of human breast carcinoma cells in the dormant stage is rather low, however some strain would be also sensitive to the treatment. This model seems to be useful in evaluating the adjuvant therapy of breast carcinoma after surgery.