CEACAM5 and cancer: Interestingly, a high detection rate was obtained using ECT2 in patients whose serum concentration of CEA was lower than the diagnostic threshold of 5 ng/mL; this was especially the case in patients with early stage cancer (ECT2 quantification sensitivity in patients with stage I/ II, stage III, and stage IV: 75%, 67%, and 59%, respectively, Figure 2D).