The sodium salt of a mixture of oligomers formed by ether and ester linkages of up to eight porphyrin units with photodynamic activity. Absorbed selectively by tumor cells, porfimer produces oxygen radicals after activation by 630 nm wavelength laser light, resulting in tumor cell cytotoxicity. In addition, tumor cell death may occur due to ischemic necrosis secondary to vascular occlusion that appears to be partly mediated by the release of thromboxane A2.