The first generation of CTC isolation instrumentation, which used the EpCAM cell surface biomarker as an immunoaffinity tag for cancer cell detection, followed up by verifying the epithelial nature of the detected cells by being DAPI-positive (i.e., having a cell nucleus), cytokeratin-positive (i.e., being epithelial), and CD45-negative (i.e., not a leucocyte), established the prognostic relevance of quantifying CTCs in 3 major late-stage cancers [6–8]. The gene discussed is PTPRC; the disease is cancer.