CYFRA 21.1 is a tumor marker primarily used to help diagnose and monitor non-small cell lung cancer (NSCLC) , particularly squamous cell carcinoma of the lungs. It is a fragment of cytokeratin 19 (a protein found in the cytoskeleton of cells) and is released into the blood when tumor cells break down.

The CYFRA 21.1 test measures the levels of this protein in the blood. Elevated levels of CYFRA 21.1 can indicate the presence of lung cancer, though it is not specific to cancer and can also be elevated in conditions such as chronic obstructive pulmonary disease (COPD) , other lung diseases , or bladder cancer .

This test is typically used in conjunction with other diagnostic tools (like imaging or biopsy) to confirm a diagnosis of lung cancer, assess the extent of the disease, and monitor the effectiveness of treatment or detect recurrence.