Patients treated in hospital for infectious mononucleosis and risk of cancer

The risk of cancer was evaluated in a cohort of 1,234 patients with severe infectious mononucleosis between 1954 and 1983. The diagnosis of mononucleosis was confirmed by reviewing patient records. The observed numbers of cancer cases up to 1988 were obtained through record linkage from the Finnish Cancer Registry, which is nationwide and population-based. There were 11 cases of cancer in the cohort, as against 17.4 expected on the basis of the 24,288 person-years at risk and of incidence rates specific for age, sex and period in the area. This gives a standardized incidence ratio of 0.6 (95% confidence interval 0.3-1.1). There was only 1 lymphoma case. No malignancies were diagnosed during the first 5 years after infectious mononucleosis. The results indicate that infectious mononucleosis with severe symptoms does not imply an increased risk of cancer.