Factors affecting spontaneous tumor incidence rates in mice: a literature review.

The recent increased use of mice for lifetime oncogenicity testing has resulted in concern for the modulating effects on spontaneous tumor incidence rates by factors other than the test article and the high variability of spontaneous tumor incidence rates in control mice. The various factors shown to affect spontaneous tumor incidence rates in mice must be considered in the planning and conduct of oncogenicity studies with this species if biologically meaningful results are to be achieved. This review reports the results of investigations conducted during the past 50 years to determine the effects of various environmental, dietary, hormonal, viral, and genetic factors on spontaneous tumor incidence rates for mice.