Multidrug resistance in human cancer. Although numerous cancers can be successfully treated with ablative surgery, radiotherapy or chemotherapy, many cancers are intrinsically resistant to anti-cancer drugs or become resistant through the course of treatment. This broad-based cellular resistance to anti-cancer drugs results, in large part, from expression of a 170 kDa multidrug transporter or P-glycoprotein, encoded by the multidrug resistance MDR1 gene in humans. Many different human cancers express the MDR1 gene at levels sufficient to confer multidrug resistance and it can be estimated that approximately 50% of human cancers will express the gene at some time during therapy.
