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Frequency and time trends of spontaneous tumors found in B6C3F1 mice oncogenicity studies over 10 years.

Historical data from 2883 B6C3F1 mice used as controls in 29 two-year oncogenicity studies terminated between 1988 and 1998 were analyzed for possible time trends in mortality, terminal body weight and tumor incidences. There was no time trend in terminal body weights. Concerning mortality data a slight decreasing trend (p > 0.05) was evident in males, whereas in females mortality rates increased significantly (p = 0.0009). The overall tumor spectrum of the collectives used was roughly in line with the tumor profile known for B6C3F1 mice. Most tumor types occurred in the hematopoietic tissue, liver, lungs, Harderian glands, vascular system, endocrinium (pituitary, adrenals and thyroids) or female reproductive organs. In comparison to literature data mice used in our lab exhibited less hepatocellular tumors and lung adenomas. Hepatocellular adenomas (females only) and carcinomas (both sexes) as well as adenomas in the Harderian glands decreased significantly over the time examined. For ovarian cystadenomas as well as uterine polyps and uterine stromal sarcomas significantly positive time trends were calculated. A positive time trend was also found for adrenal adenomas in males (p < 0.05) and histiocytic sarcomas in females (p > 0.05). Lymphomas occurred with increasing incidences over time in males (p < 0.05) and females (p < 0.05). Other factors such as genetic drifts might be responsible for these trends rather than changes in the body weights, which remained stable over 10 years.