Mesotheliomas of the tunica vaginalis propria and peritoneum in Fischer rats

Nine mesotheliomas were found in a group of 384 mature, male, Fischer-derived rats maintained on various experimental diets in long-term feeding studies. The tumors apparently were unrelated to any of the test materials. They ranged from solid, raised serosal growths to delicate papillary structures, and occurred primarily on the tunica vaginalis propria of the testis, epididymis and spermatic cord. Four of the nine cases were unusual because there was mesotheliomatous involvement of the peritoneal as well as of the genital mesothelium.