CHARACTERIZATION OF AN ESTRADIOL-INDEPENDENT BUT ESTRADIOL-RESPONSIVE GROWTH PHENOTYPE IN A HUMAN ENDOMETRIAL ADENOCARCINOMA HETEROTRANSPLANTED INTO NUDE-MICE

The tumor growth phenotype was characterized in relation to concentration of circulating estradiol, estradiol receptor (ER) activation and progesterone receptor (PgR) induction. Ten tumor pieces from an ER and PgR positive human endometrial adenocarcinoma grown in non-oophorectomized nude mice for one year were randomly selected to grow during a preparation phase of 4 weeks either in oophorectomized nude mice - to adapt tumor growth to the absence of estradiol (group A), or in non-oophorectomized nude mice (group B). For the experimental phase, tumor pieces from each group were again randomly assigned to either of two subgroups (i.e., 4 subgroups in all): with estradiol treatment (subgroups A+ and B+), or without (subgroups A- and B-) as control subgroups. There were no differences in take rate or tumor growth rate between the control subgroups (A- vs. B-), indicating tumor growth to be estradiol-independent. The tumor was estradiol-sensitive, however, as tumor growth could be stimulated by estradiol. Despite its estradiol-independence of growth, the tumor's estradiol-binding capacity varied according to whether the host animals were oophorectomized or not; and despite the similar growth patterns during the experimental phase, the values of high affinty bound ER (ER activation) were greater for tumors grown in non-oophorectomized mice during the preparation phase than for those grown in oophorectomized mice. Thus, our findings show that an ovarain (estradiol) independent but responsive phenotype of tumor growth is present in human endometrial adenocarcinomas growing in nude mice. This growth phenotype may represent an intermediate state of tumor progression to hormone independence and resistance, which has hitherto been observed only in rodent tumors.