HERVs have been implicated in autoimmune disorders,9,10 but with conflicting reports particularly involving multiple sclerosis (MS).11–13 Recent research refutes a role for deregulated HERV-W env in MS lesions, including the high-level-transcribed ERVWE1 locus encoding Syncytin-1.14 In this review, we discuss the most recent developments in the field of HERV-K and human tumor biology, in particular emerging evidence of a role for HERV-K in immunomodulation and the presence of HERV-K in tumor-derived exosomes, further indicating the potentially important role of HERV-K in human carcinogenesis. Here, ERVW-1 is linked to multiple sclerosis.