Hepatitis C infection is associated with an increased risk of non-Hodgkin lymphoma (malignancy involving lymphatic tissue) of 20 percent to 30 percent, and a three-fold increase in the risk of another type of lymphoma, according to a study in the May 9 issue of JAMA.

The prevalence of hepatitis C virus (HCV) is estimated at 1.6 percent of the U.S. population. It is more common among U.S. military veterans who use the Veterans Affairs (VA) medical system, in which approximately five percent of veterans are infected with HCV. HCV infection causes liver cancer and cirrhosis, and may also increase the risk of other tumors. Previous studies have been too small to adequately assess these risks, according to background information in the article.

Thomas P. Giordano, M.D., M.P.H., of Baylor College of Medicine and the Michael E. DeBakey Veterans Affairs Medical Center, Houston, and colleagues conducted a retrospective cohort study to test the hypothesis that HCV infection is associated with increased risk for malignancies of the blood and blood-forming tissues, related disorders, and thyroid cancer. The study involved patients from U.S. Veterans Affairs health care facilities from 1997-2004 and included 146,394 individuals infected with HCV, and 572,293 not infected with HCV. The research examined the risks of hematopoietic malignancies (relating to the formation of blood cellular components), related lymphoproliferative precursor diseases (referring to the proliferation of the bone marrow cells that give rise to lymphoid cells), and thyroid cancer.

There were 1,359 cases of non-Hodgkin lymphoma, 165 cases of Waldenström macroglobulinemia (a low grade lymphoma), 551 cases of cryoglobulinemia and 320 cases of thyroid cancer.

"We found a small but significant 20 percent to 30 percent increase in the risk of NHL [non-Hodgkin lymphoma], including all subtypes, and an almost three-fold increased risk of the low-grade lymphoma subtype Waldenström macroglobulinemia in persons with HCV infection," the authors report. Low-grade lymphoma tends to grow and spread slowly.

HCV infection was also associated with an increased risk of nonmalignant plasma cell disorders.

"We demonstrated that infection precedes development of these outcomes, and that the risk in individuals infected with HCV is consistently increased, with over five years of follow-up," the authors continue.

The study found no significantly increased risk for other hematological malignancies. The risk for thyroid cancer was not increased.

"Although the clinical significance of these findings is unknown, it is possible that screening of individuals infected with HCV could identify early stage lymphoproliferative conditions suitable for early intervention strategies, including chemoprevention trials on premalignant disease. Future epidemiological and pathophysiological studies are needed to further explore the relationship between HCV and NHL," the authors conclude.

JAMA. 2007;297:2010-2017