Effects of Hormones on Tumor Growth and Immunoreactive Insulin–like Growth Factor–1 of Estrogen Receptor–positive Human Breast Cancer (MCF‐7) Transplanted in Nude Mice

The effects of estrogens and tamoxifen were analyzed on estrogen receptor–positive human breast cancer (MCF–7) transplanted into athymic nude mice. It was found that (1) the tumor growth and the proportion of (3)H–thymidine –labeled cells were significantly increased in the 17β– estradiol dipropionate (E(2)) group, but significantly decreased In the tamoxifen (TAM) group with respect to the control group, and (2) the tumor content of insulin–like growth factor–1 (IGF–1) and the rate of IGF–1–positive cells were significantly lower in the E(2) group, but significantly higher in the TAM group than in the control group. It was concluded that the tumor content of IGF–1 and the proportion of IGF–I–positive cells were inversely correlated to the tumor growth and the (3)H–thymidine labeling index in vivo,