ABCG2 and non-small cell lung carcinoma: This finding suggests that BCRP/ABCG2-mediated drug efflux may be a common mechanism in gefitinib resistance and chemo-resistance, and raises an important issue of the timing in the use of gefitinib, a second-line therapeutic option originally approved by the U.S. FDA for advanced NSCLC patients who have failed systemic chemotherapy.