ERVW-1 and cancer: Interestingly, in addition to the similar features between syncytiotrophoblast and cancer cells (migration and invasion), several studies have found a high expression of syncytin 1, syncytin 2 and their receptors in different cancers, supporting an important function of this envelope human endogenous retrovirus (env HERV) proteins in cancer progression [122,123,124,125,126,127,128,129,130,131] (Table 1).