Syncytin-1 is also implicated in various types of cancers such as endometrial cancer, breast cancer, leukemia, urothelial cell carcinoma and human hepatocellular carcinoma, and enhances the cell proliferation, metastasis, and tumorigenicity (Yu et al. 2013; Sun et al. 2017; Chignola et al. 2019; Liu et al. 2018; Zhou et al. 2021). Here, ERVW-1 is linked to cancer.