Shionogi carcinoma 115 (SC115) tumor showed strict androgen dependency for initiation of growth. Inoculated SC115 cells showed evidence of necrosis within 5 days after implantation in the absence of androgen. After initiation of growth by androgen, the subsequent fate of SC115 tumors following androgen removal depended on the size of the tumor; small, medium, and large tumors showed complete, temporary, and no regression, respectively. In contrast with the partial and no androgen dependency of medium and large tumors in situ, tumor seeds taken from the medium and large tumors before androgen removal grew only in males when transplanted into male and female mice. On the other hand, tumor seeds taken from about one-half of the regrown tumors after androgen removal grew in both male and female hosts. One type of these androgen-independent tumors contained cytosol androgen receptor (AR) and consisted of the original SC115 cells (medullary cancer) and spindleshaped cells. Another type of independent tumor contained no cytosol AR and consisted only of spindleshaped cells. These findings seem to show that the effect of androgen depletion on the growth of tumor mass, which consists of AR-positive and androgen-dependent cells, varies in different phases of tumor growth and that the androgen dependency of tumor cells can be changed after removal of androgen. The SC115 tumor seems to be a good model for elucidating hormone-dependent cancer growth and for establishing endocrine treatment in hormone-dependent cancers.
Supported in part by Grant 201550 from the Ministry of Education, Tokyo, Japan.