Correlation between spontaneous and experimentally induced tumors in female BALB/c mice in a large...

This investigation studied the incidence of both spontaneous and induced neoplastic lesions in 6,938 BALB/c female mice receiving 0, 75, 100 or 150 ppm of 2-acetylaminofluorene (2-AAF). The mice were maintained under barrier-type, specific pathogen free/defined flora (SPF/DF) conditions, and were serially sacrificed at 9, 12, 14, 15, 16, 17, 18, 24, and 33 mon. The most frequently observed neoplasms, the incidence of which averaged over 20% and did not increase with the administration of 2-AAF, included lymphomas, alveolar-bronchiolar tumors and uterine polyps. Other common but less frequently observed neoplasms, which were also not increased by the administration of 2-AAF, included adrenocortical adenomas, angiosarcomas and ovarian, mammary and Harderian gland tumors. These spontaneous tumors accounted for almost 95% of the tumors in the control group. Conversely, induced hepatocellular and urinary bladder tumors increased in incidence with the dose level and length of administration of 2-AAF. The number of tumors per animal increased with both age and dose level of 2-AAF. After 400-500 days of life the increased incidence of induced urinary bladder and hepatocellular tumors resulted in a statistically significant increase in the ratio of tumors per animal between controls and the 150 ppm group and after 18 mon at 100 ppm. The incidence and ratio of tumors in the treated groups exclusive of bladder and liver tumors were not statistically different with those of the control group. The administration of 2-AAF did not appear to induce tumors in female BALB/c mice, except for bladder and liver tumors, and neither promoted nor inhibited the development of spontaneous tumors.