Using similar hybridization methods, Szakacs and Moscinski (13) identified the entire provirus of MMTV with a typical structure of a retrovirus [long terminal repeat (LTR), group specific antigen (gag), capsid region, polymerase (pol), reverse transcription region, and envelope (env) in 7 (13%) of 52 human breast cancers]. The gene discussed is ERVW-1; the disease is breast cancer.