Using PCR techniques directed at a 660 bp highly conserved portion of the MMTV-env gene with only 16% homology to the prototype HERV-K10 human endogenous retrovirus, Wang et al. were able to demonstrate MMTV- env specific sequences in 38.5% of the 314 breast carcinomas and in 6.9% of the 29 breast fibroadenoma samples, compared to only 1.8% of 107 samples of normal breast reduction mammoplasty tissues [15]. Here, ERVW-1 is linked to breast carcinoma.