Mueller et al. (2018) uncovered that yolk sac tumor cells expressed pluripotency markers LIN28A and showed an intermediate level of HERV-K env mRNA higher than somatic differentiated germ cell tumor cells. Moreover, HERV-K gag protein can be detected by immunoblotting in tumor biopsies (Herbst et al., 1996). Significantly higher levels of anti-HERV-K gag and anti-HERV-K env can be observed in serum samples taken from patients with yolk sac tumor (Kleiman et al., 2004; Curty et al., 2020). This evidence concerns the gene ERVW-1 and yolk sac tumor.