An odd finding piqued the interest of Ann-Sofi Duberg, MD, of Örebro University Hospital, Örebro, Sweden, and colleagues. Four otherwise healthy young Swedes came down with non-Hodgkin's lymphoma. Their only risk factor: hepatitis C infection.
Hepatitis C can cause liver cancer, but its role in blood cell and bone marrow cancers is controversial. The researchers say that in general, risk factors for these cancers are related to an altered or weakened immune system such as from HIV or medications that suppress the immune system.
Duberg's team looked at medical records for 27,150 residents of Sweden who, from 1990-2000, learned they had hepatitis C infection.
Compared to the number of cancers one might expect, non-Hodgkin's lymphoma was nearly twice as common in people with hepatitis C infection. Another cancer -- multiple myeloma, a cancer of plasma cells in the bone marrow - was 2.5 times more common in people with hepatitis C than would be expected.
Because for many patients there was a delay in diagnosing hepatitis C infection, the researchers note that they may have underestimated the actual cancer risk.
How could a liver virus cause lymph and marrow cancers? That isn't clear. It's possible that since hepatitis C is a blood-borne virus, some as-yet-unknown cancer-causing agent got into the patients' bloodstreams.
On the other hand, there's also evidence that the hepatitis C virus may get into the cells that become lymph tissues and blood.
There was some good news from the study. Hepatitis C infection does not seem to increase a person's risk of several other cancers: thyroid cancer, chronic lymphatic leukemia, acute lymphatic leukemia, and Hodgkin's lymphoma.
Duberg and colleagues report their findings in the March 2005 issue of Hepatology.