Hepatitis C virus infection and risk of multiple myeloma: Evidence from a meta-analysis based on 17 case-control studies.

Hepatitis C virus (HCV) infection is a leading cause of chronic liver damage and is associated with other diseases. Some studies reported that patients with HCV have a significantly increased risk of multiple myeloma while others do not report an association. We aimed to clarify the association between HCV and multiple myeloma and analyse the factors that affect the controversial conclusions through a meta-analysis. We conducted a systematic literature search of HCV and myeloma in the databases of PubMed/MEDLINE, Cochrane Library, EMBASE, Wanfang and China National Knowledge Infrastructure (CNKI) from inception to September 2016. Outcomes were expressed as odds ratios (ORs) and 95% confidence intervals (95% CIs). A positive correlation between HCV infection and risk of developing multiple myeloma was revealed (OR=2.67, 95% CI=1.35-5.26, P=.005) based on meta-analysis of 17 case-control observational studies. When the data were stratified by source of control, significant associations were observed in hospital-based studies, but not population-based studies. Further subgroup analyses showed increased risk of multiple myeloma in HCV patients when studies were conducted in high HCV prevalent countries, but not in low or moderate HCV prevalent countries. In addition, similar positive association was detected in studies performed in the East Asia and in intermediate-quality studies. In summary, the association of HCV infection with increased risk of multiple myeloma depended on several factors, including study design, quality and environmental HCV prevalence. Further large-scale, well-designed studies are needed to validate the role of HCV in the aetiology of multiple myeloma.