People infected with the hepatitis C virus (HCV) are at an increased risk of developing certain lymphomas (cancers of the lymphatic system), according to a study published in the May 8, 2007, issue of the "Journal of the American Medical Association".

Researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, and Baylor College of Medicine, found that HCV infection increased the risk of developing non-Hodgkin's lymphoma by 20 per cent to 30 per cent. The risk of developing Waldenström's macroglobulinemia (a rare type of non-Hodgkin's lymphoma) went up by 300 per cent and the risk for cryoglobulinemia, a condition marked by abnormal levels of certain antibodies in the blood, was also elevated for those with HCV infections.

The researchers looked at patient records collected from Veterans Affairs (VA) hospitals across the United States between 1996 and 2004. Researchers selected more than 700,000 records; 146,394 represented patients who were diagnosed with the hepatitis C virus, while 572,293 represented patients who were not. Based on that review, researchers determined, first, that the patients infected with HCV had a higher risk of developing lymphoma and, second, that HCV infection preceded development of the lymphoma. The risk of lymphomas in HCV-infected patients was charted across more than five years of follow-up.

"This is one of the largest studies ever conducted to look at the relationship between hepatitis C virus infection and cancers of the lymphatic system," said NCI Director John E. Niederhuber, M.D. "Since so much is still unknown about the causes of lymphoma, establishing which factors contribute to the disease is the first step in finding ways to reduce its incidence and lessen mortality."

HCV causes hepatitis, which is an inflammation of the liver. The HCV virus is carried through the blood and is passed from person to person through the exchange of bodily fluids - via shared needles, open wounds, and sexual contact, and other means. HCV is also known to cause cirrhosis and liver cancer.

"Although the risk of developing lymphomas is small, our research suggests that screening of HCV-infected individuals could identify conditions which may lead to cancer. It might then be possible to prevent progression to lymphoma," said investigator Eric A. Engels, M.D., from the Viral Epidemiology Branch of NCI's Division of Cancer Epidemiology and Genetics. "More research is needed to further clarify the relationship between HCV infection and lymphoma."

In the United States, there are more than 4.1 million people living with hepatitis C virus infection - about 1.6 per cent of the population. In 2007, it is estimated that 71,380 Americans will be diagnosed with some type of lymphoma, which will take 19,730 lives.

The researchers note that this study was limited to military veterans who used the VA system, so the results may not be applicable to the overall US population. The study population was mostly men (97 percent), the majority of patients were white, and the average age was 52 years. Patients in the HCV-infected group were more likely to have served during the Vietnam era (1964-1975) than were uninfected patients in the comparison group.

Previous studies found that the prevalence of HCV infection is much higher among US veterans who use the VA medical system (5 %) than in the general population, where only 1.6 per cent carry the virus. Several factors have likely contributed to this higher prevalence, including demographics, socioeconomic status, and particularly a history of injection drug use or blood transfusions received before 1990, when screening for hepatitis C virus was started.