Cytokeratins are epithelial markers whose expression is not lost during malignant transformation. Cyfra 21-1 is a cytokeratin-19 fragment that is soluble in serum and may be a useful circulating tumor marker. Cyfra 21-1 is a sensitive and specific tumor marker of NSCLC, especially of squamous cell subtype. It also reflects the extent of the disease and has an independent prognostic role along with performance status and disease stage in NSCLC