Does P-glycoprotein predict response to chemotherapy?

Why some cancers are curable by chemotherapy while most are not is an enigma and a major challenge for cancer researchers. The use of anticancer drugs in appropriate dosages and combinations has improved response rates and prolonged life. Yet, it is not uncommon for a patient to have a relapse during a course of chemotherapy that was initially successful. The discovery more than a decade ago that resistance to unrelated drugs is relatively common among variant cells isolated in vitro has led to speculations that similar multidrug-resistant (MDR) tumor cells arise in vivo and that selective growth of such cells leads to a disease that is nonresponsive even to a combination of different anticancer drugs (1). That such a scenario might account for the lack of response observed in some patients has spawned an area of active research (a) to elucidate the mechanism of multidrug resistance and (b) to test critically the hypothesis that the presence of MDR tumor cells limits successful chemotherapy.