 Such newly developed materials include the increasingly interesting expansible, high biocompatibility microspheres in polyvinyl alcohol and co-acrylic acid with the following novel features capable of enhancing anticancer effects: 1 they are not reabsorbable, and induce permanent embolization; 2 being deformable they adapt to the morphology of the vessels to be embolized, and selectively target cancerous arterial capillaries: 3 they deliver greater quantities of chemotherapy agent, minimizing systemic effects thereof. 