PTPRC and nasopharyngeal carcinoma: Previously, we established the CTC enrichment protocol based on cell-size separation, which is able to isolate viable and label-free CTCs in our laboratory using a spiral microfluidics CTC chip and the downstream workflow for CTC enumeration.16 Figure 1a shows the image of representative CTCs defined by DAPI+/CK+/CD45− staining from a NPC patient.