Background Serum expression of cytokines may provide information about the clinical outcome of advanced non-small cell lung cancer (NSCLC) patients.This study aimed to investigate the relationship between serum cytokine levels and the clinical outcome of erlotinib treatment in a second or third line setting in patients with advanced NSCLC.Methods A total of 162 patients with advanced NSCLC who received erlotinib as either second or third line therapy were enrolled in this study.Blood samples were collected before the initiation of erlotinib treatment,and the levels of IL-1,IL-2R,IL-6,and tumor necrosis factor (TNF)-α were assessed by enzyme-linked immunosorbent assay (ELISA).Cutoff points were defined as the median levels of IL-1 (low (≤26.5 pg/ml) and high (＞26.5 pg/ml)),IL-2R (low (≤115 pmol/L) and high (＞15 pmol/L)),IL-6 (low (≤49.5 pg/ml) and high (＞49.5 pg/ml)),and TNF-α (low (≤48.5 pg/ml) and high (＞48.5 pg/ ml)).Kaplan-Meier analysis was used to estimate the survival time,and Cox regression analyses were used to correlate cytokines and baseline clinical characteristics with clinical outcomes,including time to progression (TTP) and overall survival (OS).Results Between January 2007 and May 2011,162 patients were enrolled.Their median age was 58 years.In this group,109 were males and 53 were females,74 were former or current smokers and 88 were non-smokers.A total of 122 patients had adenocarcinoma,27 had squamous cell carcinoma,and 13 had tumors with other types of histology.And 139 patients had an East cooperative oncology group (ECOG) performance status of 0-1,while 23 scored at 2-3.Expression of IL-1,IL-2R,and IL-6 was not significantly associated with age,gender,ECOG performance status,smoking status,or histology and stage of tumor.Only TNF-α was associated with smoking status (P=0.045).Survival analysis showed that patients with low levels of either IL-6 or TNF-α had a statistically longer TTp and OS than patients with high expression (P ＜0.05).These cytokines remained significant upon multivariate analysis (P ＜0.05).Conclusion IL-6 or TNF-α may serve as potential predictive biomarker for the efficacy of erlotinib.