P-glycoprotein (P-gp/ABCB1): Overexpressed in multiple cancers such as acute myeloid leukemia, gliomas, hepatocellular carcinoma, and small cell lung cancer, P-gp reduces intracellular concentrations of chemotherapeutic agents, including paclitaxel, doxorubicin, and vincristine. Here, ABCB1 is linked to small cell lung carcinoma.