Testicular mesotheliomas in rats exposed to N-2-fluorenylacetamide (FAA)

The incidence of testicular mesotheliomas after exposure to the carcinogen N-2-fluorenylacetamide (FAA) was studied in Fischer 344 rats. The animals were fed a carcinogenic diet (containing 0.06% FAA) for 4 weeks and then a control diet for 1 week. This schedule was carried out for 3 complete cycles (12 weeks). A smaller group of rats was treated with FAA for 1 complete cycle only (4 weeks). One group of untreated controls was also available. The surviving rats were sacrificed at 59 weeks of age. The administration of FAA for 3 complete cycles resulted in a high incidence of liver, testis and Zymbal-gland tumors. The testicular tumours were mesotheliomas and occurred in 9/25 rats. No such tumour was observed in animals treated for 1 cycle only or in untreated controls. The high incidence of testicular mesotheliomas, a rare type of tumour in this and other rat strains, suggests an association with the treatment. The present experimental model may be useful in elucidating the mechanisms of the induction of mesothelial tumours of the testis by chemical carcinogens.