Thymic tumors induced by 3-methylcholanthrene treatment of rat Peyer's patches

Studies were performed to characterize thymic tumors which were induced after a single injection of 500 microgram or 3-methylcholanthrene (3-MC) into surgically exposed Peyer's patches (PP) of Copenhagen rats. Detailed gross, histological, and morphological analyses revealed thymic tumors differing in size and weight (1 to greater than 8 g) with distorted architecture and infiltration by lymphocytes and epithelial cells in varying proportions. Approximately 25% of the rats with thymic tumors exhibited abnormal spleens, whereas 66% developed low grade leukemias. A majority of the thymic tumors contained cells which exhibited (1) phenotypic markers characteristic of normal thymocytes, (2) abnormal DNA, and (3) increased percentages in S + G2 phases of the cell cycle. Further studies of tumor cell isolates demonstrated an increased frequency of colony formation on soft agar, as well as the ability to elicit thymic tumors upon transplantation. Collectively these studies describe chemically induced thymic lymphomas.