The Env protein sequence is 645 aa long, and has the highest amino acid identity with the Env protein of an infectious MuLV isolated from a human small cell lung cancer line NCI-417 [32] and MuLV New Zealand Black 9–1 xenotropic retrovirus (NZB-9–1) [28]), 95% and 94%, respectively. This evidence concerns the gene ERVW-1 and small cell lung carcinoma.