Relationship between incidence and onset age of mammary tumours and uterine adenomyosis in four strains of mice: comparison with the findings of 40 generations previously.

Like most characteristics studied in research, mammary tumourigenesis and uterine adenomyosis in mice are regulated by both genetic and environmental factors and information about the degree of participation of each factor in these lesions is important in the use of mice for investigations. Several parameters on spontaneous mammary tumours and uterine adenomyosis in four strains of mice with different potentials for these lesions were compared in those before and after more than 40 generations or more than 10 years (1987). During these periods, the mice were exposed to several different intangible or unavoidable environmental factors, although they are quite stable genetically by maintenance with full-sib mating. Nevertheless, small differences were observed between the present and 1987 regarding strain-related characteristics, such as the onset age, the cumulative incidence and the growth of mammary tumours and uterine adenomyosis. It is suggested that genetics is more influential than environmental factors regarding the maintenance of strain-related characteristics of mammary and uterine lesions.