Interestingly, env genes were also found significantly over-expressed in primary tumors or cancer cell lines including envK (HML2) in germ cell tumor lines [31], melanoma [32], breast cancer [33] and ovarian cancer tissue [34]; Syncytin-1 over expression was found in breast cancer tissue [35], EnCa [8, 9], colon carcinoma [36], and leukemia and lymphoma [37]. Here, ERVW-1 is linked to breast cancer.