Abstract
A spontaneous ovarian cystadenocarcinoma with papillary growth to the serosa in a 66-week-old F344 rat was investigated morphologically and compared with a rat abdominal mesothelioma. Macroscopically, a large white soft mass was found in the right ovarian area with disseminated small nodules to the serosa and cloudy bloody-ascites in the abdominal cavity. Metastases to the lungs and lymph nodes were noted. Histologically, major growth patterns of the ovarian mass were tubular, cystic and/or papillary. The tubular areas were characterized by atypical cuboidal and/or columnar epithelial cells, with various amounts of stroma dividing glands. Cystic areas consisted of single or multiple cysts lined by uniform epithelial cells with intra-cystic papillary growth, supported by abundant hyaline-like stroma. Continuing from the ovarian mass, tumor cells were spread on the mesentery and omentum. Superficially, papillary projections resembling those of a mesothelioma were apparent. In deep areas, tubular structures consisting of epithelial cells were surrounded by various amounts of connective tissues. In the mesothelioma, collagen fibers were diffusely distributed around clustered or individual tumor cells. Since the histologic features strongly suggested a derivation from ovarian surface epithelium, we diagnosed this case as an ovarian cystadenocarcinoma with papillary growth to the serosa. Immunohistochemical results did not provide any clear specific reactions to distinguish ovarian cystadenocarcinomas from mesotheliomas.
