[Highly metastatic mammary tumors in M. m. musculus Sub-Jyg (JYG mouse)]

The present paper reports the highly metastasis of mammary tumors in Chinese wild mouse M. m. musculus Sub-Jyg (JYG mouse), which was recently inbred at the National Institute of Genetics, Mishima, Japan. The incidence of mammary tumors at 18th generation was 89% at about 9 months of age. Histology of mammary tumors in 19 cases examined were medullary or papillary adenocarcinoma (Comedo type) with highly anaplastic features. Metastasis was found not only in the lungs (53%), but also in the liver (21%) and spleen (16%), respectively. MMTV antigen and particle were also found in various organs by immunoperoxidase method and electronmicroscopy. As a result of present observation, JYG mouse was considered to be a unique model in the study of the metastasis of mammary tumors to the liver and spleen.