Histopathology of ovarian tumors in two groups of rats. Formalin-fixed tumors were sectioned and stained to determine cellular origin of the respective tumor and analysed in a blinded fashion by a pathologist. Representative tumor samples are shown as adenocarcinoma (A), sarcoma (B), squamous carcinoma (C), and granulosa cell tumor (D). Adenocarcinoma cells are arranged with glandular structures in back-to-back nests which are separated by Lumina. The nuclear/cytoplasmic ratio is high in these cells. The nucleus shows obvious pleomorphism, granular chromatin, and large plump nuclei with prominent nucleoli. Sarcoma cells are arranged in bundles and streams and are in an overall spindle shape. Multifocal squamous cell differentiation with marked keratinization are observed in squamous carcinoma. The tumor cells were microscopically similar to granulosa cells of normal follicles and numerous mitosis suggested a rapid growth in granulosa cell tumor. (H & E stain, 200×).