The immunohistochemical evaluation of estrogen receptor-alpha and progesterone receptors of normal, hyperplastic, and neoplastic endometrium in 88 pet rabbits

The expression of estrogen receptor-alpha (ER) and progesterone receptor (PR) in normal, hyperplastic, and neoplastic endometrium in rabbits was evaluated by immunohistochemistry. The tissues evaluated were 27 normal uteri, 19 cases with endometrial hyperplasia, and 42 adenocarcinomas. Sixteen of 27 cases of normal uteri (59.3%) and 13 out of 19 hyperplasias (68.4%) stained positive with both ER-alpha and PR. Adenocarcinomas were further subdivided into 26 papillary and 16 tubular/solid adenocarcinomas. Papillary adenocarcinoma infiltrated the myometrium late in the disease and caused attenuation of the myometrium. In contrast, tubular/solid adenocarcinoma invaded into the deep myometrium early in the disease without thinning of the myometrium. Twenty-one cases out of 26 (80.8%) cases of papillary adenocarcinoma were both ER-alpha and PR negative, whereas 15 out of 16 (93.8%) of the tubular/solid adenocarcinomas were positive for ER-alpha, PR, or both. The total immunoreactive scores of ER-alpha, PR, and mode of myometrial invasion were significantly different between histopathologic types. This suggests that there may be 2 different developmental pathways for uterine adenocarcinomas in the rabbit.