Factors influencing augmentation and/or acceleration of lymphoreticular tumors in mice by benzo(a)pyrene treatment

The response of lymphoreticular tissues to a single i.p. injection of benzo(a)pyrene was studied in the first generation of C57BL/6J X C3HeB/FeJ F1 and C3HeB/FeJ X A/J F1 mice. Groups of 1-, 15-, and 42-day-old animals of both sexes received 75 or 150 mug of the carcinogen per g body weight. After a period of approximately 90 weeks, a high incidence (up to 43%) of reticulum cell sarcomas was observed in C57BL/6J X C3HeB/FeJ F1 mice treated with benzo(a)pyrene at 40 days of age. Animals treated with carcinogen at younger ages had a lower incidence of reticulum cell sarcomas. These sarcomas showed marked cellular pleomorphism and were classified into histiocytic, epitheloid-nodular, reticulocytic, and fibrocytic forms according to the predominant cell type. Lymphomas of thymic and extrathymic lymphoid origin and leukemia of granulocytic type were seen in a descending order of frequency. Control animals of either strain that were killed at 90 weeks of age were basically free of lymphoreticular tumors, while those kept under observation up to 170 weeks developed these tumors in 24% (C57BL X C3H F1) and 10% (C3H X A/J F1), respectively. Studies revealed that the augmentation and/or acceleration of development of the lymphoreticular neoplasms and specifically reticulum cell sarcomas by benzo(a)pyrene was dependent upon the strain and sex of mice used and the age at which the animals were exposed to carcinogen.