A regimen consisting of vincristine, dactinomycin and cyclophosphamide, which is used for the treatment of rhabdomyosarcoma (RMS) and ovarian germ cell tumors. OR An abbreviation for a chemotherapy combination used to treat rhabdomyosarcoma in children. It is also used to treat certain types of ovarian germ cell tumors. VAC regimen includes the drugs vincristine sulfate, dactinomycin (actinomycin-D), and cyclophosphamide. Also called VAC.