Search for mouse mammary tumor virus-like env sequences in cancer and normal breast from the same individuals

We have reported previously that a 660-bp sequence homologous to the env ge ne of the mouse mammary tumor virus, but not to the known endogenous retrov iruses, was present in 38% of human breast cancers (Y. Wang et al., Cancer Res., 55: 5173-5179, 1995), A unique 250-bp internal sequence was equally p resent in formalin-fixed breast carcinoma. It was not detected in normal hu man breasts or in other tumors, In this study, we have investigated whether this 250-bp env sequence was also present in the formalin-fixed normal tis sues of individuals with env sequence-positive breast cancer, Separate para ffin-embedded sections from breast carcinoma and normal breast tissues from the same individual were obtained from the Cooperative Breast Cancer Tissu e Registry of the National Cancer Institute. The 250-bp env sequence was de tected in 30.1% of the 106 tumors but in only 1 of the 106 normal breast ti ssues, These results indicate that the sequence is absent in normal tissues and thus is not genetically transmitted. This strongly implies that it is of exogenous origin.