ERVW-1 and endometrial polyp: In concert with other ERV-env genes Syncytin-1 represented: 1) the single highest expressed gene in EnCa; 2) was among the most significant six env genes in a comparison of all three cohorts; 3) along with Syncytin-2 and erv-3 co-localized to endometrial polyp, hyperplastic and tumor epithelial cells pointing to a functional role in this cell type; 4) was significantly associated with both tumor staging and growth patterns; and 5) along with other ERV-env family members was regulated by methylation.