What is a tumor marker?
A tumor marker is a substance — usually a protein — measurable in blood, that some cancers produce in above-normal amounts. Familiar examples: PSA (prostate), CEA (bowel and others), CA 19-9 (pancreas and bile duct), CA-125 (ovary), AFP (liver), LDH (lymphoma and general tumour activity).
The single most important fact
Most tumor markers are better at tracking a known cancer than at finding one. Levels rise and fall with treatment response, so a falling marker during chemotherapy is encouraging and a steady rise can flag recurrence early. But as detection tools they are blunt: benign conditions raise them, and some cancers never raise them at all.
Why a raised marker is not a diagnosis
- Inflammation, infections, smoking, liver disease and benign cysts can all elevate markers.
- Ranges overlap: a mildly raised value occurs in many healthy people.
- The reverse also holds — a normal marker does not rule cancer out.
That is why no reputable guideline diagnoses cancer from a marker alone; imaging and biopsy make the diagnosis, markers help follow it.
Reading the trend, not the number
One value is a dot; the direction over time is the information. Ask three questions:
- What was my baseline before treatment?
- Is the trend falling, flat, or rising across several measurements?
- Was each test done in the same lab? (Different assays give different absolute numbers.)
Frequently asked questions
My marker doubled — should I panic? Not from one reading. Labs vary and single spikes happen; the standard move is a confirmatory retest and, if the rise persists, a scan.
Are there markers that ARE diagnostic? A few come close in the right context (very high AFP in a liver mass, for instance), but context is everything — which is exactly what your own doctors weigh.
Can you review my marker history? Yes — attach your lab results to a ticket and we will chart the trend and explain it against your treatment timeline.