Background: Elevated levels of serum C-reactive protein (CRP) have been reported to have prognostic significance in lung cancer patients. This study aimed to further identify CRP-bound components as prognostic markers for lung cancer and validate their prognostic value.
Methods: CRP-bound components obtained from the serum samples from lung cancer patients or healthy controls were analyzed by differential proteomics analysis. CRP-bound serum amyloid A (CRP-SAA) was evaluated by co-immunoprecipitation (IP). Serum samples from two independent cohorts with lung cancer (retrospective cohort, 242 patients; prospective cohort, 222 patients) and healthy controls (159 subjects) were used to evaluate the prognostic value of CRP-SAA by enzyme-linked immunosorbent assay.
Results: CRP-SAA was identified specifically in serum samples from lung cancer patients by proteomic analysis. CRP binding to SAA was confirmed by co-IP in serum samples from lung cancer patients and cell culture media. The level of CRP-SAA was significantly higher in patients than in healthy controls (0.37 ± 0.58 vs. 0.03 ± 0.04, P < 0.001). Elevated CRP-SAA levels were significantly associated with severe clinical features of lung cancer. The elevation of CRP-SAA was associated with lower survival rates for both the retrospective (hazard ration [HR] = 2.181, 95% confidence interval [CI] = 1.641-2.897, P < 0.001) and the prospective cohorts (HR = 2.744, 95% CI = 1.810-4.161, P < 0.001). Multivariate Cox analysis showed that CRP-SAA was an independent prognostic marker for lung cancer. Remarkably, in stages I-II patients, only CRP-SAA, not total SAA or CRP, showed significant association with overall survival in two cohorts. Moreover, univariate and multivariate Cox analyses also showed that only CRP-SAA could be used as an independent prognostic marker for early-stage lung cancer patients.
Conclusion: CRP-SAA could be a better prognostic marker for lung cancer than total SAA or CRP, especially in early-stage patients.