Risk of Hodgkin's disease and other cancers after infectious mononucleosis

Background: Infectious mononucleosis, which is caused by the Epstein-Barr v irus, has been associated with an increased risk for Hodgkin's disease. Lit tle is known, however, about how infectious mononucleosis affects longterm risk of Hodgkin's disease, how this risk varies with age at infectious mono nucleosis diagnosis, or how the risk for Hodgkin's disease varies in differ ent age groups. In addition, the general cancer profile among patients who have had infectious mononucleosis has been sparsely studied. Methods: Popul ation-based cohorts of infectious mononucleosis patients in Denmark and Swe den were followed for cancer occurrence. The ratio of observed-to-expected numbers of cancers (standardized incidence ratio [SIR]) served as a measure of the relative risk for cancer. SIRs of Hodgkin's disease in different su bsets of patients were compared with the use of Poisson regression analysis . All statistical tests including the trend tests were two-sided. Results: A total of 1381 cancers were observed during 689619 person-years of follow- up among 38562 infectious mononucleosis patients (SIR = 1.03; 95% confidenc e interval [CI] = 0.98-1.09). Apart from Hodgkin's disease (SIR = 2.55; 95% CI = 1.87-3.40; n = 46), only skin cancers (SIR = 1.27; 95% CI = 1.13-1.43 ; n = 291) occurred in statistically significant excess. In contrast, the S IR for lung cancer was reduced (SIR = 0.71; 95% CI = 0.58-0.86; n = 102). T he SIR for Hodgkin's disease remained elevated for up to two decades after the occurrence of infectious mononucleosis but decreased with time since di agnosis of infectious mononucleosis (P for trend <.001). The SIR for Hodgki n's disease tended to increase with age at diagnosis of infectious mononucl eosis (P for trend =.05). Following infectious mononucleosis, the SIR for H odgkin's disease at ages 15-34 years was 3.49 (95% CI = 2.46-4.81; n = 37), which was statistically significantly higher than the SIR for any other ag e group (P for difference = .001). Conclusion: The increased risk of Hodgki n's disease after the occurrence of infectious mononucleosis appears to be a specific phenomenon.