ERVW-1 and neoplasm: We could test the hypothesis for an env-induced immune-stealth cloak in transmissible cancers by implementing the methods used to discover and characterize syncytins [23,24,139–141]: in silico search for co-opted (or recently introduced) retroviral env genes within the tumour genomes, and in vitro verification of expressed and upregulated Env proteins in the tumour.