[Age-related incidence of spontaneous tumors in SPF C57BL/6 and BDF1 mice].

Incidence of spontaneous tumors in C57BL/6 NCrj (CR), C5BL/6 CrSlc (SL) and B 6 Crj x DBA/2 NCrj F1 (BD) mice, which were reared under a barrier system and died natural death, were examined. Cohorts of mice in 200 to 300 each were purchased at 4 weeks of age and raised under SPF conditions. A large portion of the mice were used for various experiments between 3 and 30 months old while not a small number died before use and were autopsied. Median survival periods of the female and male were estimated at 697 and 680 days for CR, 764 and 806 days for SL and 866 and 929 days for BD, respectively. Incidence of spontaneous neoplastic lesions in the autopsied animals were 77.4% and 79.2% of 535 female and 590 male CR, 69.7% and 55.1% of 502 female and 463 male SL, and 75.8% and 78.0% of 298 female and 346 male BD, respectively. In CR, histiocytic sarcoma was the most predominant tumor, accounting for 72.1% of all tumors. In SL, malignant lymphoma was the most prevailing, forming 62.3%, and, in male BD, hepatocellular carcinoma was the most frequent, accounting for 41.8% of all tumors.