Some aspects of the search for a human mammary tumor virus

T been used as a model in the search for a human breast cancer virus. Milk from the inbred Parsi community of Bombay, which ]has an unusual cancer-site pattern with a I-elatively high incidence of breast cancer, was compared with milks from two groups of American donors-women with a familial breast cancer association and "control" women with no familial history of breast cancer. In an extended search, virus-like (type B) particles structurally similar to or identical with those responsible for transmitting mammary tumors in mice have been found in 39% of 46 Parsi milks, 31% of 101 milks of "highrisk" American families, and 12% of 181 "'controls." Sera from women who had had breast cancer showed a significant neutralizing effect on the mouse virus, whereas control sera had