Hepatitis B and C viruses and risk of non-Hodgkin lymphoma: a case-control study in Italy

Non-Hodgkin lymphomas (NHLs) are the most frequent haematological malignancies, representing 3 % of all new cancer cases worldwide [1]. In Europe, NHLs represented the 11th most common neoplasm, with around 93,500 new cases diagnosed in 2012. Among European countries, Italy shows one of the highest age-standardized incidence rates in both men and women [2].

Although the etiology of most NHL cases is still unknown, human immunodeficiency virus (HIV) and other infectious agents such as Epstein-Barr virus, human herpesvirus 8, human T-lymphotropic virus type I, and Helicobacter pylori are the best documented causes of specific types of NHL [3, 4].

Despite the etiologic heterogeneity among NHL subtypes [5], a consistent association between hepatitis C virus (HCV) infection and NHL has been well established over the last two decades [3, 6, 7], suggesting that, globally, approximately 8 % of NHL may be attributable to HCV [8]. Few studies have evaluated the possible role of hepatitis B virus (HBV) infection as a risk factor for NHL and showed positive association in some but not all instances [9]. Furthermore, the majority of these investigations lacked information on the complete panel of antigen and antibody markers of HBV infection [10–12].

To further elucidate the relationship between HBV and HCV infections and the risk of NHLs, we expanded a case-control study, which had started in 1999, in different areas of Italy [13]. Special care was put into exploring a comprehensive HBV serologic panel to allow a well-defined assessment of its role in the risk of developing NHL.

The data in the present study were derived from two consecutive case-control studies on lymphomas, conducted with similar study protocols in the periods 1999–2002 [13] and 2003–2014.

Approximately 60 % of both NHL cases and controls tested negative for any HBV serologic markers (Table 2). The prevalence of HBsAg seropositivity was 3.7 % among NHL cases and 1.7 % among controls, leading to an OR of 1.95 (95 % CI: 1.00–3.81) for HBsAg⁺ individuals compared to people susceptible to HBV infection. Immunity due to natural infection (i.e., HBsAg⁻/anti-HBs⁺/anti-HBc⁺), immunity due to vaccination (HBsAg^-/anti-HBs⁺/anti-HBc^-), and the positivity for anti-HBc alone (HBsAg⁻/anti-HBs⁻/anti-HBc⁺) were not significantly associated with NHL risk. Chronic co-infection of HBV and HCV was reported in only one NHL case.

The findings from this large case-control study confirmed the well-established association between HCV infection and NHL, highlighting the potential favorable role of prevention and treatment of HCV infection. The study also provided further evidence on the role of HBV infection in NHL etiology, reporting a 2-fold significantly elevated risk of B-cell NHL in HBsAg⁺ people. No increased risk emerged among people immunized because of past infection or vaccination, or among those who tested positive for anti-HBc alone.

Although chronic HCV infection has been associated to NHL since the early 1990s [17, 18], the International Agency for Research on Cancer definitely linked it to NHL etiology only in 2009 [3]. These findings were further supported by a recent pooled analysis of case-control studies from the InterLymph Consortium [5], which reported an 1.8-fold increase in NHL risk for anti-HCV⁺ people.

Although anti-HCV-positivity was associated to NHL risk, we found that only individuals with circulating HCV RNA were actually at increased risk for NHL, indicating that only persistent chronic HCV infection is associated to lymphomagenesis. This finding is in agreement with a previous large multicenter case-control study from EPILYMPH [19], which found a statistically significant association between NHL and detectable HCV RNA (OR = 1.82, 95 % CI: 1.13–2.91).

The association with HCV-positivity was found for a broad range of B-cell NHL subtypes, with a high prevalence of chronically infected NHL patients (13–29 %) in our study. Our results are in agreement with several studies that found an association of HCV with DLBCL, MZL, LPL, and SLL/CLL [7, 19–24]. At variance with a previous study [25], no significant association emerged between HCV infection and Burkitt lymphoma. Prior studies have produced mixed results for T-cell NHL [6], but no significant relationship with HCV infection emerged from our study.

The association between HCV infection and B-cell NHL found in this study is consistent with the evidence that proliferation of specific B-cell clones, caused by chronic antigenic stimulation induced by HCV, plays a role in the pathogenesis of B-cell lymphomas [26]. In fact, continuous stimulation of the immune system by HCV may lead to molecular alterations in the lymphocytes, immune dysregulation, and eventually B-cell [27].

HBV infection has been studied less frequently than HCV infection in relation to NHLs, and most of the evidence is based on case–control studies [3, 9]. Furthermore, although a comprehensive testing of HBV antigens and antibodies is required to assess the HBV status, only few studies considered the complete HBV serological panel. In our study, a two-fold increased NHL risk was found among HBsAg⁺ patients. The association was statistically significant for B-cell NHL. A previous Italian study on B-cell lymphomas [28] reported complete information on HBV serology, showing a pattern of association between HBV status and NHL very similar to our present findings. Conversely, non-significant associations were reported by the Epilymph case-control study [29] for both chronic and past HBV infections.

The majority of the studies have considered the HBV markers separately, most of them resting on HBsAg. Findings on HBsAg⁺ have been associated to a 1.5-to-4-fold increase in NHL risk [10, 12, 13, 30, 31]. Seropositivity to anti-HBc alone has been investigated quite rarely as a marker of past HBV infection, reporting a moderate or non-significant association with NHLs [12].

Although our results should be interpreted with caution as they are based on a relatively small number of HBV carriers, we found that HBsAg⁺ patients had an elevated risk for B-cell NHL and, particularly, DLBCL. In agreement with our results, a multicenter case-control study [28] found a higher prevalence of HBsAg⁺ among patients with DLBCL or FL than among controls. In South Korea, a large cohort study [30] showed that HBsAg-positivity was associated with an increased risk of DLBCL, but not with FL.

The association of NHL, and predominantly of B-cell lymphoid malignancies, with active chronic HBV infection, though not with past exposure, suggests that HBV might promote B-cell lymphomagenesis in a way similar to that proposed for HCV (i.e., chronic antigen stimulation of B-cells), possibly enhanced by engagement of B-cell surface receptors and co-stimulatory molecules [6].

The presence of occult HBV infections – i.e., the presence of circulating HBV DNA in HBsAg⁻/anti-HBs⁻ patients – is a relevant concern in etiological studies, since it may lead to biased results. Occult HBV infection was, however, rare in our study population. In a companion study on HCC, all HBsAg⁻/anti-HBs⁻ cases and controls were screened for HBV DNA [14]. HBV DNA was detected in one HCC case out of 85 HBsAg⁻/anti-HBs⁻/anti-HBc⁻ study subjects (1.2 %) and in one HCC case out of 36 HBsAg⁻/anti-HBs⁻/anti-HBc⁺ subjects (2.8 %). Both cases were co-infected with HCV.

Interpretation of study findings should take into account some limitations. First, hospital-based case-control studies are prone to selection bias in the inclusion of hospital controls. However, the prevalence of HBV and HCV positivity in the control group was consistent with the findings of previous surveys of hepatitis virus prevalence in Italy [32]. Furthermore, individuals admitted to hospital for diseases related to alcohol and tobacco consumption, or hepatitis viruses and autoimmune diseases, were excluded. Second, despite the relatively large sample size, the study has still limited power to detect association for specific NHL subtypes. Third, people with anti-HCV⁻ were not tested for HCV RNA. Although an underestimation of HCV prevalence cannot be completely ruled out, no excess of NHL risk emerged among anti-HCV⁺/HCV RNA⁻ people. Accurate testing for serological detection of HCV/HBV in a centralized laboratory and the revision of NHL diagnosis represent important strengths of our study.

Our case-control study confirmed the association between HCV infection and risk of NHL, including the major NHL subtypes. Furthermore, our results lent additional support to the possibility that chronic HBV infection may also have a role in the development of B-cell NHL. Prevention and treatment of HCV and HBV infection is increasingly possible and may diminish NHL incidence, notably in areas with high prevalence of infection with hepatitis viruses.