After screening all selected probes, GAPDH as a marker of global cellularity and VIL1 as a marker of intestinal epithelial origin, both normalized to CD45 as a marker of unspecific non-CTC immunoisolation, were included in a statistical model that efficiently discriminated between metastatic colorectal cancer patients and controls. The gene discussed is PTPRC; the disease is metastatic colorectal cancer.