Overexpression of ABCG2 has been studied and correlated to MDR phenotypes of numerous cancer cell lines derived from tumor types such as SN-38-selected human small cell lung cancer cells PC-6/SN2-5, mitoxantrone-selected human gastric carcinoma cell line EPG85-257RNOV, gefitinib-resistant non-small cell lung cancer (NSCLC) cells, epirubicin-resistant human hepatocyte carcinoma cells HLE-EPI, topotecan and doxorubicin-selected human multiple myeloma cells (Mo and Zhang, 2012). The gene discussed is ABCG2; the disease is cancer.