Adenomatoid tumor--like structures in the subperitoneal nodules produced by sex steroids.

Multiple subperitoneal nodules were produced in the abdominal cavities of guinea pigs treated with various doses of estradiol benzoate for 3 months. Gland-like structures with intervening fibrous stroma were observed in 20% of these nodules. These gland-like structures resembled adenomatoid tumors, but were composed of cells that resembled mesothelium, ciliated cells, and cells with mucin in the cytoplasm. Some parts were composed of cells that had a squamous appearance. In guinea pigs, pretreatment with estradiol benzoate followed by treatment with a combination of estradiol benzoate and progesterone for 1 to 3 months produced nodules with gland-like structures similar to those produced by estrogen treatment alone. However, the gland-like structures were composed only of cells that resembled mesothelium and cells with cilia. Therefore, we conjecture that the formation of gland-like structures in the subperitoneal nodules is the result of mesothelial inclusions and their proliferation and that some of these mesothelial cells were differentiated into ciliated, mucinous, and squamous cells by estrogen.