Background
Hepatitis C virus (HCV) infection has been associated with several extrahepatic manifestations. Oral cancer is one of them. We investigated the association among oral squamous cell carcinoma (OSCC), multiple primary cancers (MPCs), insulin resistance and HCV infection.
Material and Method
Upper gastrointestinal tract examination and determination of the presence of HCV infection were routinely done for 60 primary OSCC patients. Occurrence of MPCs was evaluated between 1992 and 2008.
Results
Of the 60 patients, 21 (35%: 15 males and 6 females; mean age 67.3+/-11.9 years) developed MPCs. Antibodies to HCV were found in 26.7% (16/60) of cases. The incidence of MPCs in HCV-infected OSCC cases was 62.5% (10/16 cases, P<0.01 vs the non-HCV-infected OSCC group); for cases without HCV infection it was 25% (11/44 cases). In HCV-infected cases, 10 MPCs with patients, hepatocellular carcinoma (HCC) was the most common outcome (5 cases), whereas gastric cancer was the most common outcome (6 cases) in non-HCV-infected 11 MPCs. In logistic regression analysis, the adjusted odds ratios on staging IV, anti-HCV positive, and over 70 years old were 15.50, 13.45, and 4.46, respectively, indicating that there were significant differences. Furthermore, the patients with HCV-infected MPCs had hyperinsulinemia.
Conclusions
HCV infection was strongly associated with the occurrence of MPCs as well as primary OSCC. HCV-infected OSCC patients in Japan should receive medical treatment to inhibit development of HCC. In patients with HCV infection, it is important to clinically examine organs other than the liver.

Keywords: Neoplasms, Multiple Primary - virology, Multivariate Analysis, Mouth Neoplasms - virology, Insulin Resistance, Hepatitis C - pathology, Hepacivirus - metabolism, Carcinoma, Squamous Cell - virology, Aged, 80 and over, Risk Factors