current chemotherapeutic approaches for cancer are in part limited by the inability of drugs to destroy neoplastic cells within poorly vascularized compartments of tumors . we have here systematically assessed anaerobic bacteria for their capacity to grow expansively within avascutar compartments of transplanted tumors . among 26 different strains tested , one appeared particularly promising . we created a strain of c . novyi devoid of its lethal toxin and showed that intravenously injected c . novyi - nt spores germinated within the avascular regions of tumors in mice and destroyed surrounding viable tumor cells . when c . novyi - nt spores were administered together with conventional chemotherapeutic drugs , extensive hemorrhagic necrosis of tumors often developed within 24 hours , resulting in significant and prolonged anti - tumor effects . this strategy , called combination bacteriolytic therapy , has the potential to add a valuablle dimension to the treatment of cancer .