Occult blood and tumour markers in bowel cancer detection: a narrative review by class of marker

Description

Bowel cancer usually bleeds before it hurts, long before anyone notices. That is why screening programmes post out a stool test that measures human haemoglobin, and why a positive sample buys a colonoscopy. The test is cheap enough to run a country on, but it misses tumours that were not bleeding on the day the sample was taken, and most of the people it flags turn out to have nothing. So there is a search for something to measure alongside it: proteins shed by a tumour, altered DNA in stool or in blood, signs of the immune response. Which of them add anything to a haemoglobin result is unsettled. The studies test different markers at different cut-offs, some in screening populations and some in symptomatic clinics, and they confirm what they found against anything from colonoscopy in everyone to a cancer registry checked two years later. This review takes that literature one class of marker at a time and asks the same questions of each study: measured in whom, checked against what, and what did it change about who was sent for a camera. Reading comes first, before anybody writes.

Student responsibilities

Read up on bowel cancer detection and on how a test is judged. Take one class of marker, read the studies that report it, build the table that goes with them, and write that section of the review.