[Experimental chemoendocrine therapy of human breast carcinoma xenograft serially transplanted into nude mice]

The antitumor effect of combined chemoendocrine therapy with tamoxifen (TAM) and 5-fluorouracil (5-FU) on breast carcinoma xenograft (R-27), serially transplanted into the nude mice, was examined from the aspect of estrogen receptors (ER) and cytological features. The mice were given 6 intramuscular injections of TAM (5mg/kg) at 3-day intervals (TAM group), 3 intraperitoneal injections of 5-FU (60 mg/kg) at 4-day intervals ((5-FU group), or a combination of the two drugs (combined group). When the tumor was resected on 21 days after the initial treatment, the ER were assayed and %S was determined by flowcytometry. Furthermore, proliferative cell nuclear antigen (PCNA) was stained, and the stained cells were counted. A synergistic antitumor effect of TAN and 5-FU was found in mice given combined therapy. Reduction in the ER level was more marked in this group than in the others, but there were no significant differences in the %S value or the ratio of PCNA positive cells among the three treated groups. These results suggest that the combined effect of TAM and 5-FU has no relation to the inhibition of DNA synthesis.