We have investigated the experimental combined chemo- and endocrine therapy of UFT and tamoxifen (TAM) on two human breast carcinoma xenografts, R-27 and Br-10 with estrogen receptors (ER) serially transplanted into nude mice. When sc inoculated tumor started the exponential growth, the treatments were initiated in four groups which were control, UFT 20 mg/kg (as tegafur) po daily for 18 times, TAM 5 mg/kg im twice a week for 6 times and UFT + TAM groups. The antitumor activity of the agents were assessed by the growth curves, the lowest T/C ratios of the relative mean tumor weight and the actual tumor weights at the end of the experiments. TAM alone was effective on both R-27 and ineffective on Br-10, while UFT alone was ineffective on R-27 and Br-10. The combination antitumor activity was observed in R-27 but not in Br-10. When 5 mg of TAM per kg and 20 mg of UFT per kg as tegafur was administered daily po for 2 wk, there were no statistically significant differences between the concentration of 5-FU in UFT alone and UFT + TAM groups for the two strains. By the assay of ER and progesterone receptors using the same specimen, it was observed that ER was stable by the treatment of UFT, while ER was suppressed by the treatment of TAM in both tumor strains. In addition, this suppression of ER by TAM alone was enhanced by the combined treatment with UFT in both the strains.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals Breast Neoplasms