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[Purpose] Complement component 7 (C7) is a member of the complement system,which participates in the formation of Membrane Attack Complex.People with component C7 deficiency are prone to bacterial infection,but the relationship between the abnormalities of component C7 and cancer have not been well defined.The aim of this study is to analyze the role of component C7 in non-small cell lung cancer (NSCLC).[Methods] Protein expression of component C7 in lung cancer cells was analyzed by Western blot.Component C7 expression was induced by lentivirus transfection in lung cancer cells with component C7, and its function on colony formation was further evaluated.One hundred and seventy-three NSCLC tumor samples,tumor-adjacent tissues and normal tissues were collected at Zhejiang Cancer Hospital in China between 2006 and 2011, and mRNA expression of component C7 was analyzed by RT-PCR.Associations of the gene expression with clinicopathological factors, progression free and overall survival were evaluated.[Results] Western blot showed component C7 expression was low or null in A549, NCI-H460,NCI-H1395 and SK-MES lung cancer cell lines.Component C7 was overexpressed in SK-MES cells which also showed reduced colony formation.Moreover,the mRNA expression of component C7 was gradually reduced from normal lung tissues,to tumor-adjacent tissues and tumor tissues (P<0.001),and the expression of component C7 was inversely correlated with tumor grade or clinical stage in NSCLC (P=0.027 and P=0.000, separately).NSCLC patients with lower component C7 had an increased risk of disease recurrence or death compared with those who had higher C7.The hazard ratio (HR) was 0.43 for relapse (95% confidence interval [CI], 0.18~1.01,P=0.053) and 0.29 for death (95%CI,0.10~0.82,P=0.019) after adjusting for age at diagnosis, gender, grade, stage,histology and smoking status.Kaplan-Meier survival analysis demonstrated similar results.[Conclusions] Component C7 seems to play an important role in the progression of lung cancer and it may serve as an independent predictive marker for the prognosis NSCLC patients.Further investigation of this molecule in lung cancer is needed.