Coordenação de Aperfeiçoamento de Pessoal de Nível Superior ( CAPES ), Fundação de Amparo à Pesquisa do Estado de Pernambuco ( FACEPE ; outorga: APQ-1554-4.01 / 15 ) e Conselho Nacional de Desenvolvimento Científico e Tecnológico ( CNPq ; outorga: 409681 / 2016- 4 )The complement system (CS) is a key element of immunity against pathogens but also seems to influence other events, such as tumorigenesis and tissue repair. Complement component 7 (C7) is a key component of the lytic pathway of CS, leading to the formation of the membrane attack complex (MAC). This study aimed to investigate the existence of the association of a polymorphism in the C7 gene, rs1063499, with hepatic fibrosis and the occurrence of hepatocellular carcinoma (HCC) in patients with hepatitis C. We analyzed 456 samples from patients with chronic hepatitis C. Real-time PCR was used for allelic discrimination. Patients were classified by their METAVIR score as F1 (n = 100), F2 (n = 83), F3 (n = 101) or F4 (n = 66); 106 patients were diagnosed with HCC. Patients carrying the G/G genotype of C7 had a lower chance of developing severe fibrosis in the recessive model (p = 0.042; OR: 0.65 95% CI 0.41-1.02). However, the G/G genotype frequency was higher in patients with HCC (P = 0.01; OR: 2.07 95% CI 1.20-3.53) and in those with larger tumors (p = 0.04). The G/G C7 genotype seems to be a protective factor against advanced fibrosis; however, it was associated with a higher risk of HCC and the occurrence of larger hepatic nodules, suggesting the involvement of C7 in the physiopathogenesis of HCC and fibrosis in patients with hepatitis C virus (HCV).2050-01-01