Mammary tumors, plaques, and hyperplastic alveolar nodules in various combinations of mouse inbred strains and the different lines of the mammary tumor virus

The following strains have been bred and developed for mammary tumor studies in this laboratory; C3H, C3HfB, C3HfDD, C3H‐A vy , C3H‐A vy fB, DD, DDfB, DDfC3H, BALB/c, BALB/cfDD, BALB/cfC3H, A (High), A (Low), AfB, and C57BL. Data are presented on mammary tumor incidence and age, occurrence of plaques, and occurrence of hyperplastic nodules. C3H‐A vy is our highest mammary tumor strain, whereas C57BL is the most resistant. A complete range of mammary tumor incidences and average ages depending upon the strain of mouse and line of virus is found in the other strains. The occurrence of mammary tumors in strains fostered on C57BL ranges from an incidence of 90% at an average age of 15 months in C3H‐A vy fB, although there is no evidence of any milk‐transmitted virus, to 1.3% at 16.5 months in AfB. We continue to find an incidence of 20% at 17 months in BALB/c although we have no conclusive evidence of the virus. C3H virus has a greater potency than DD virus. Plaques are the result of DD or BALB/c genotype and DD virus but not of C3H or A genotype or of C3H or A virus. Hyperplastic nodules appear in all strains that develop mammary tumors, the age at which they appear depending upon the mouse strain and line of virus. These data form the foundation for other studies with these strains. The strains are now available to other investigators.