To determine if the differential response to PD0332991 in the melanoma cell lines is due to drug effiux we tested the effect of an inhibitor of the drug effiux pumps P-glycoprotein and breast cancer resistance protein (BCRP), in two cell lines which displayed resistance to PD0332991, SK-Mel-2 and WM115. The gene discussed is ABCG2; the disease is melanoma.