Serum amyloid A protein: a potential biomarker correlated with clinical stage of lung cancer.

Objective: To identify serum diagnosis or progression biomarkers in patients with lung cancer using protein chip profiling analysis.

Method: Profiling analysis was performed on 450 sera collected from 213 patients with lung cancer, 19 with pneumonia, 16 with pulmonary tuberculosis, 65 with laryngeal carcinoma, 55 with laryngopharyngeal carcinoma patients, and 82 normal individuals. A new strategy was developed to identify the biomarkers on chip by trypsin pre-digestion.

Results: Profiling analysis demonstrated that an 11.6 kDa protein was significantly elevated in lung cancer patients, compared with the control groups (P < 0.001). The level and percentage of 11.6 kDa protein progressively increased with the clinical stages I-IV and were also higher in patients with squamous cell carcinoma than in other subtypes. This biomarker could be decreased after operation or chemotherapy. On the other hand, 11.6 kDa protein was also increased in 50% benign diseases of lung and 13% of other cancer controls. After trypsin pre-digestion, a set of new peptide biomarkers was noticed to appear only in the samples containing a 11.6 kDa peak. Further identification showed that 2177 Da was a fragment of serum amyloid A (SAA, MW 11.6 kDa). Two of the new peaks, 1550 Da and 1611 Da, were defined from the same protein by database searching. This result was further confirmed by partial purification of 11.6 kDa protein and MS analysis.

Conclusion: SAA is a useful biomarker to monitor the progression of lung cancer and can directly identify some biomarkers on chip.