CXCR4 and nonpapillary renal cell carcinoma: To date, studies have shown that HIF-2α, TWIST, and CXCR4 are overexpressed in several human tumors such as clear cell renal carcinoma (ccRCC) [23], nonsmall cell lung cancer (NSCLC) [24], neuroblastoma [25], and breast, prostate, gastric, hepatocellular, colon, and bladder cancers [11–18].