Characteristics of Hodgkin's lymphoma after infectious mononucleosis.

Infectious mononucleosis-related Epstein-Barr virus (EBV) infection has been associated with an increased risk of Hodgkin's lymphoma in young adults. Whether the association is causal remains unclear. We compared the incidence rates of Hodgkin's lymphoma in two population-based Danish cohorts of patients who were tested for infectious mononucleosis: 17,045 with serologic evidence of having had acute EBV infection, and 24,614 with no such evidence. We combined the cohort of patients who had serologically verified infectious mononucleosis with a cohort of 21,510 Swedish patients with infectious mononucleosis (combined total, 38,555). Biopsy specimens of Hodgkin's lymphomas occurring during follow-up in this combined cohort were tested serologically for the presence of EBV. Using this information, we modeled the relative risk of EBV-negative and EBV-positive Hodgkin's lymphoma in different periods after the diagnosis of infectious mononucleosis and estimated the median incubation time for mononucleosis-related EBV-positive Hodgkin's lymphoma. Only serologically confirmed infectious mononucleosis was associated with a persistently increased risk of Hodgkin's lymphoma. Sixteen of 29 tumors (55 percent), obtained from patients with infectious mononucleosis, had evidence of EBV. There was no evidence of an increased risk of EBV-negative Hodgkin's lymphoma after infectious mononucleosis. In contrast, the risk of EBV-positive Hodgkin's lymphoma was significantly increased (relative risk, 4.0; 95 percent confidence interval, 3.4 to 4.5). The estimated median incubation time from mononucleosis to EBV-positive Hodgkin's lymphoma was 4.1 years (95 percent confidence interval, 1.8 to 8.3). A causal association between infectious mononucleosis-related EBV infection and the EBV-positive subgroup of Hodgkin's lymphomas is likely in young adults.