New research finds that people chronically infected with hepatitis B virus (HBV) are nearly two times as likely to develop non-Hodgkin lymphoma (NHL).

HBV is already known to cause liver cancer -- around 340,000 cases globally each year -- and some researchers have suspected it might cause lymphoma, a cancer of the blood. Hepatitis C is also linked to lymphoma.

The U.S. National Cancer Institute's Dr. Eric Engels and Sun Ha Jee, of Yonsei University in Seoul, examined the records of more than 600,000 people in South Korea, where HBV was widespread before a mass vaccination campaign began in 1995. Approximately 9 percent of patients, 53,000, had evidence of HBV infection. After 14 years, infected patients had an increased risk of NHL, 19.4 cases per 100,000 person-years compared to 12.3 per 100,000 among those who did not have HBV.

NHL is not common and hepatitis B vaccination efforts are unlikely to affect NHL rates much, the researchers noted. But it may be possible to treat HBV and help NHL patients, they said.

Scientists think both hepatitis B and hepatitis C cause lymphoma by over-stimulating the immune system as it tries to fight the virus. An estimated 350 million people worldwide are infected with HBV, which kills between 500,000 and 1.2 million people annually.

The report, "Hepatitis B Virus Infection and Risk of Non-Hodgkin Lymphoma in South Korea: A Cohort Study," was published early online in the Lancet Oncology (2010;doi:10.1016/S1470-2045(10)70167-4).