Its most useful role in surveillance is after R0 resection in colorectal cancer, but has limitations as a marker of recurrence, as elevations of CEA can be seen in several non-neoplastic conditions, as active inflammation of the colon and rectum, renal or hepatic insufficiency, end-stage lung diseases, hypothyroidism, obesity, aging, and cigarette smoking29, 30, 31, 32, 33. Here, CEACAM5 is linked to obesity due to melanocortin 4 receptor deficiency.