MMTV-like env gene sequences in human breast cancer

We have previously detected an MMTV env gene-like 660 bp sequence in 38% of human breast cancers, but not in normal tissues or other tumors. In this c ommunication we report the sequences from eleven tumors and three breast ca ncer cell lines, and compare them to four strains of MMTV and to the known endogenous retroviral sequences. The breast cancer sequences were highly ho mogenous to the MMTV's, but not to the endogenous sequences suggesting an e xogenous origin.