Distribution of mammary gland neoplasms and factors influencing metastases in hybrid mice.

Mammary neoplasms in yellow (C3H x VY-A vy) F-1 virgin female mice with the murine mammary tumor virus were distributed equally between the left and right sides. The ratio of thoracic to inguinal gland involvement was 6.4 to 3.6 indicating that the A vy mutation, which enhances age-specific mammary tumor incidence, apparently does not affect the distribution of mammary tumors. The average tumor size was similar in all mammary glands. Multiple tumors occurred seven times more frequently in the thoracic than in the inguinal glands. Metastases occurred more frequently in moribund mice than in those killed at a scheduled time, and the incidence of pulmonary metastases in both groups was associated with the duration of the mammary tumors, their size, their location, and the number of neoplasms. Adenocarcinomas in the thoracic glands metastasized to the lungs more frequently than those in the inguinal glands.