Although a circulating tumor cell is classically defined as expressing epithelial markers such as EPCAM and cytokeratin (CK) and lacking the leukocyte marker CD45, the presence of CTCs with both epithelial and leukocyte markers (dual-positive cells, DP cells, CK+/CD45+) in the blood of cancer patients has recently been reported. This evidence concerns the gene PTPRC and neoplasm.