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Abstract
In the beginning of the nineties the National Cancer Institute Surveillance, Epidemiology, and End Results Program calculated the incidence of primary central nervous system non-Hodgkin's lymphoma (PCNSL) as 1:100000. The incidence of PCNSL has been increasing since the seventies in immunocompetent patients. The main increase, however, is taking place since the mid-eighties and is due to the increase of immunodeficiency and immunosuppression. The risk is 2-6% in AIDS patients according to clinical data and will probably further increase with the length of survival in these patients. Transplant patients carry a risk of 1-5% to develop a PCNSL. The risk is 1-2% for renal, and 2-7% for cardiac, lung or liver transplant recipients. Patients with congenital immune deficiency have a risk of 4%. PCNSL may also present as a secondary malignancy.