The effect of
Tamoxifen (TAM) on
tumor growth was investigated experimentally using ovarian
dysgerminoma serially transplanted into nude mice. The mice were divided into two groups according to
estrogen receptor (ER) content of initially transplanted
tumor; groups TAM-A and -B indicated ER rich and ER poor
tumor, respectively. Their own control (CNT) was included in each group. After TAM treatment, the
tumor size of TAM-A and -B groups was 150 fold and 350 fold that of initial
tumor respectively, while that of group CNT was over 500 fold, suggesting that a strong anti-
tumor effect of TAM was exerted especially on ER rich
tumor. Histological changes following
tamoxifen treatment such as a decline in the size of
tumor cells and nuclei as well, and a decrease in the mitotic index were observed only in the TAM-A group. The concentration of ER and
progesterone receptor (PR) in the cytosol of these
tumors were measured. The ER levels in the initial
tumor tissue of TAM-A and -B were 14.7 and 3.3 fmol/mg
protein, respectively. The significant increase in PR content in TAM-A following TAM administration obviously indicated a so-called TAM-dependent PR induction effect. These results indicated that
ovarian cancer containing ER, even though it originated from germ cells, would be responsible for
antiestrogen therapy.