Estradiol induced changes in tumor growth and steroid receptor content in a heterotransplanted human endometrial adenocarcinoma.

To study the importance of estrogen availability to growth pattern and other tumor characteristic such as estrogen receptor (ER) and progesterone receptor (PgR) content and histopathology, we have used a human tumor-nude mouse model, in which an ER- and PgR-positive and estradiol-sensitive (stimulated) human endometrial adenocarcinoma was heterotransplanted and serially passed in female (non-oophorectomized) nude mice over a period of one year. Pieces from this tumor were transplanted into oophorectomized nude mice, randomly divided into two groups, one with and one without estradiol treatment (preparation phase). After four weeks, pieces from both these groups were again transplanted into oophorectomized nude mice, each group being randomly allocated to two subgroups, one with and one without estradiol treatment (experimental phase). Tumor growth was measured during the experimental phase, whereas both ER and PgR content and histopathology were analyzed after the experimental phase. Our findings indicate that even short-term growth under estradiol-poor conditions can trigger such progressive changes as reduced steroid receptor content, development of a less differentiated tumor and tendency to enhanced tumor growth. On the other hand, estradiol-rich conditions enhanced ER activation, PgR induction and tumor differentiation in the same tumor line. The estrogenic conditions under which a tumor grows may thus be crucial determinants of tumor progression.