Cell fusion between M13SV1 breast epithelial cells and the triple-negative breast cancer cell lines HS578T, MDA-MB-231 and MDA-MB-435S was observed after coculturing between wild-type cells with or without TNFα as inflammatory stimulus, but it was also induced by the overexpression of Syncytin-1 in the epithelial cells or inhibited by the knock-out (KO) of ASCT2. The gene discussed is TNF; the disease is triple-negative breast carcinoma.