The highest increased fold differences in env expression were observed in samples from dogs diagnosed with chronic myelomonocytic leukemia, melanoma, and osteosarcoma, with 2−ΔΔCt values of 22.02-fold (DCML-0401), 48.51-fold (DMEL-1101), and 1,402.29-fold (DTM-1401), respectively. This evidence concerns the gene ERVW-1 and melanoma.