Background: 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.
Study objective: The aims of this study were (1) to confirm sensitivity and specificity of Cyfra 21-1 in detecting non-small cell lung cancer (NSCLC) and especially the squamous cell subtype, (2) to assess the potential relationship between Cyfra 21-1 and disease stage of the disease in NSCLC, and (3) to evaluate prognostic effect of Cyfra 21-1 in NSCLC.
Methods: An immunoradiometric assay of serum Cyfra 21-1 was performed in 161 patients with lung cancers and 71 others with benign lung diseases. The ability of Cyfra 21-1 to detect different histologic subtypes of lung cancer vs benign lung diseases was assessed through receiver operating characteristic (ROC) curves and comparisons with other tumor markers such as carcinoembryonic antigen, neuron-specific enolase, and squamous cell carcinoma antigen. Comparisons of Cyfra 21-1 levels according to histologic subtype and disease stage were done using Kruskal-Wallis test. Independent prognostic value of Cyfra 21-1 was studied with a multivariate analysis of survival (Cox's model).
Results: Using a threshold of 3.3 ng/mL for Cyfra 21-1, sensitivity and specificity were, respectively, 0.59 and 0.94 in NSCLC, 0.68 and 0.94 in the subgroup of the squamous cell carcinoma, and 0.19 and 0.94 in small cell lung cancer. Cyfra 21-1 levels were significantly higher in advanced NSCLC than in early-stage disease. All 29 patients with serum concentrations >32 ng/mL had stage IIIB-IV and only one of 14 patients with stage I-II disease had Cyfra 21-1 level >18 ng/mL. In the multivariate analysis of survival, Cyfra 21-1 was an independent prognostic factor along with performance status and disease stage in NSCLC.
Conclusions: 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.
Implications: A high level of Cyfra 21-1 in apparently early-stage NSCLC should be an indication for more extensive workup before thoracotomy. The independent prognostic role of Cyfra 21-1 level may be useful in stratifying populations with advanced NSCLC or early-stage resected NSCLC as elevated Cyfra 21-1 levels might identify those patients at high risk for treatment failure.