Extranodal lymphomas constitute a heterogeneous group of malignancies, accounting for roughly 60% of all non-Hodgkin lymphomas. The extranodal organ where lymphomas arise is an important determining factor of biological, molecular, and aetio-pathogenic features, and of presentation, dissemination pattern, and outcome. An increased risk of CNS involvement, an uncommon but lethal event, has been suggested in some extranodal lymphomas, but the absolute risk is still debatable for most of these malignancies. This debate is because of the presence of selection biases and other confounding factors in related literature, which inevitably has led to conflicting recommendations. The identification of extranodal lymphomas at increased risk of CNS dissemination is an important unmet clinical need; affected patients could benefit from early CNS assessment by neuroimaging and cerebrospinal fluid analysis and adequate CNS prophylaxis, avoiding unnecessary prophylaxis and related toxicity in low-risk patients. This Review discusses relevant confounding factors and identifies high-risk extranodal lymphomas analysing histopathological category, involved organ, and other specific risk factors, which could be helpful for result interpretation and patient stratification in future clinical trials. Finally, a recommendation is provided for CNS-directed management of high-risk extranodal lymphoma patients in daily practice.
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