bThe impact of the HCV genotype 1b core amino acid (aa) 70 mutant on the cumulative rate of hepatocellular carcinoma following eradication of HCV RNA by antiviral therapy was investigated with the Q-Invader assay. Multivariate analysis based on 649 patients indicated that a core aa70 Q-Invader mutant level >20% is a predictor of hepatocellular carcinoma. P revious reports indicated that amino acid (aa) substitutions at position 70 in the hepatitis C virus (HCV) core region in patients infected with HCV genotype 1b (HCV-1b) are pretreatment predictors of poor virological response to antiviral therapy (1, 2) and also affect hepatocarcinogenesis, regardless of treatment response (3-7). In particular, hepatocellular carcinoma (HCC) still occurs even after eradication of HCV RNA by antiviral therapy (8-12), and substitutions of aa70 at the start of antiviral therapy also affect hepatocarcinogenesis following eradication of HCV RNA (13).Recently, Tadokoro et al. (14) reported the results of a comparative quantitative analysis of aa70 substitution in the HCV-1b core region by the real-time PCR monitoring Invader reaction (Q-Invader assay; BML, Inc., Saitama, Japan). This highly sensitive assay (based on the Q-Invader technology using mutant-specific primers) was developed to determine the relative ratio of the aa70 mutant (glutamine/histidine) to the aa70 wild-type (arginine) virus. The assay in that study (14) detected a minor type plasmid that constituted only 1% of a mixture of plasmids containing wild-type and mutant sequences. In this study, we evaluated the associations between core aa70 Q-Invader mutant levels at the start of antiviral therapy and HCC following eradication of HCV RNA.Among 5,023 consecutive patients infected with HCV in whom antiviral therapy (interferon monotherapy, interferon plus ribavirin combination therapy, or triple therapy of NS3/4A protease inhibitor plus peginterferon plus ribavirin) was initiated between February 1987 and June 2013 at Toranomon Hospital, 2,121 patients infected with a single genotype of HCV-1b, -2a, or -2b were selected for this retrospective study. All patients achieved sustained virological response, defined as negative HCV RNA at 24 weeks after cessation of antiviral therapy, based on HCV RNA qualitative analysis (Amplicor; Roche Diagnostics, Manheim, Germany) or by the Cobas TaqMan HCV test (Roche Diagnostics, Tokyo, Japan), and they were free of HCC before and during interferon therapy. The cumulative rate of HCC was calculated using the Kaplan-Meier technique; differences between the HCC rate curves were tested using the log-rank test. The period between the end of antiviral therapy and the diagnosis of HCC was used for group-based statistical analysis of HCC. Stepwise Cox regression analysis (multivariate analysis) was used to determine independent factors associated with HCC. This study protocol was in compliance with the Good Clinical Practice guidelines and the 1975 Declaration of Helsinki, and it was approved by the institutional review board at Toranomon ...