current approaches for treating cancer are limited , in part , by the inability of drugs to affect the poorly vascularized regions of tumors . we have found that spores of anaerobic bacteria in combination with agents which interact with microtubules can cause the destruction of both the vascular and avascular compartments of tumors . two classes of microtubule inhibitors were found to exert markedly different effects . some agents that inhibited microtubule synthesis , such as vinorelbine , caused rapid , massive hemorrhagic necrosis when used in combination with spores . in contrast , agents that stabilized microtubules , such as the taxane , docetaxel , resulted in slow tumor regressions that killed most neoplastic cells . remaining cells in the poorly perfused regions of tumors could be eradicated by sporulated bacteria . mechanistic studies showed that the microtubule destabilizers , but not the microtubule stabilizers , radically reduced blood flow to tumors , thereby enlarging the hypoxic niche in which spores could germinate . a single intravenous injection of spores plus selected microtubule - interacting agents was able to cause regressions of several tumors in the absence of excessive toxicity .