We found that, in chemo-resistant U87RETO glioblastoma cells, cytotoxic stress induced by etoposide promotes accumulation and large-scale fission of mitochondria, associated with the detection of HERV-WE1 (syncytin-1) and HERV-FRD1 (syncytin-2) in these organelles. Here, ERVW-1 is linked to glioblastoma.