MCM4 as a prognostic biomarker of early-stage lung cancer.

e21033 Background: Prognostic biomarker in early-stage lung cancer is less well defined. Despite early detection, one-third of patients with completely resected early-stage lung cancer without lymph node involvement have a recurrence. Our main objective is to investigate potential biomarkers useful in classification and predicting prognosis of this early-stage lung cancer, particularly in lymph node-negative subgroup. Methods: In discovery phase, we performed proteomic profiling on 60 lung cancer tissues to distinguish solid versus non-solid adenocarcinoma. Relative protein quantification was analyzed using Tandem Mass Tag mass spectrometry. In validation phase, tumor tissues from an additional cohort were analyzed by immunohistochemistry in conjunction with quantitative image analysis to confirm the differential expression of significantly altered proteins, including MCM2, MCM4, MCM6, SCAMP3, DPP4 and MYH11. Prognostic potentials of each biomarker were analyzed with univariate and multivariate analyses. Results: Quantitative proteomic analysis of predominantly solid versus non-solid adenocarcinoma tissues showed 30 differentially expressed proteins consisting of 13 increased and 17 decreased proteins found in solid compared with non-solid adenocarcinoma. Four most increased proteins (MCM2, MCM4, MCM6, and SCAMP3) and two most decreased proteins (DPP4 and MYH11) were selected for immunostaining in the validation cohort of 204 patients with resected adenocarcinoma without lymph node involvement. 57 out of 204 (27.9%) patients had recurrent disease. The high expression level of MCM4 was the strongest signature for disease recurrence (HR 4.85, 95%CI 2.78-8.47, p < 0.0001) and remained significant under multivariate analyses adjusted for TNM stage, histologic subtypes, lymphovascular invasion, tumor necrosis, and adjuvant chemotherapy. Recurrence-free survival (RFS) was significantly shorter in patients with high MCM4 compared with low MCM4 (5-y RFS 50% vs 84%, p < 0.0001) and remained highly significant within stage IA (5-y RFS 69% vs 93%, p < 0.0001), or stage IB and II (5-y RFS 36% vs 69%, p = 0.001). High expression of MCM4 correlated with other poor prognosis factors including smoking (p = 0.001), stage (p = 0.003), lymphovascular invasion (p = 0.036), visceral pleural invasion (p = 0.005), tumor necrosis (p < 0.0001) and solid histology (p < 0.0001). Conclusions: High MCM4 expression serves as an important prognostic biomarker predicting recurrence in early-stage node-negative lung adenocarcinoma.