CYFRA 21-1 (lung cancer marker)
A fragment of a structural protein (cytokeratin 19) released by some lung cancer cells into the blood. Its main use is to help monitor non-small-cell lung cancer that is already diagnosed — following treatment response and disease activity over time, not as a screening test.
What it measures
CYFRA 21-1 measures a fragment of cytokeratin 19, one of the structural proteins that form the internal scaffolding of epithelial (surface-lining) cells. When lung cancer cells — particularly those of non-small-cell lung cancer, and especially the squamous type — break down and turn over, these fragments are released into the blood, so the level tends to reflect the amount of active tumour. Its established role is in monitoring known non-small-cell lung cancer: in someone being treated, a falling CYFRA 21-1 suggests the treatment is working, while a rising trend across serial measurements can be an early clue that the disease is progressing, prompting imaging and reassessment. It is not a screening test and is not used to make a diagnosis on its own, because it is not specific to cancer — modest elevations can occur with benign lung disease and other conditions, and it can be normal in early cancer. It is often measured together with other lung markers (CEA, NSE, SCC antigen) because different lung tumour types raise different markers, and the specialist interprets the pattern within the full clinical picture.
What a high value can mean
- Non-small-cell lung cancer — the main use; higher levels reflect more active disease and are followed during treatment.
- A rising trend in known lung cancer — can signal the disease progressing.
- Benign lung disease — pneumonia, other lung conditions can cause modest, non-cancer rises.
- Reduced kidney function — can raise the level independently.
- A single mildly raised value — often non-specific and needs the trend and clinical context.
What a low value can mean
- Normal or low — the expected result, and reassuring during monitoring.
- A falling level during treatment — suggests the therapy is working.
- Not a rule-out — a normal CYFRA 21-1 does not exclude lung cancer.
When to discuss with a doctor
CYFRA 21-1 is a specialist monitoring marker for non-small-cell lung cancer, not a screening or stand-alone diagnostic test. In someone with known lung cancer it is followed over time — a falling trend is reassuring, a rising trend prompts imaging and reassessment. Outside that setting a mildly raised value is often non-specific, from benign lung disease or reduced kidney function, and a normal value never rules cancer out. It is usually read together with other lung markers because different tumour types raise different ones. Mediora.AI can surface a CYFRA 21-1 trend and show it alongside related markers, but this needs specialist assessment — the interpretation belongs with your oncology team.