ABCB1 and neoplasm: However, successful treatment is limited by the ability of tumor cells to gain resistance to chemotherapeutic agents resulting in relapse of the disease for a variety of reasons including overexpression of P-glycoprotein [19], mutations in tubulin that alter microtubule assembly [20–22] and altered tubulin composition resulting from changes in the production of tubulin isotypes [23] and microtubule associated/interacting proteins [24, 25].