Several factors hinder the identification of risk factors for central nervous system (CNS) involvement in diffuse large B-cell lymphoma (DLBCL), including the retrospective nature of most studies, the relatively low frequency of CNS relapse in DLBCL, and the heterogeneity of CNS prophylaxis methods used in these studies. Moreover, the impact of newly developed diagnostic tools (such as multiparameter flow cytometry [FCM]) and new treatments introduced in the last decade, in particular rituximab, has still not been fully clarified.Several studies 4,5,[7][8][9][10] and a recent meta-analysis 1 have described a decrease in rates D iffuse large B-cell lymphoma patients have a 5% overall risk of central nervous system events (relapse or progression), which account for high morbidity and frequently fatal outcomes, 1 and shortened overall survival of <6 months.2 Early diagnosis of central nervous system events is critical for successful treatment and improved prognosis. Identification of patients at risk of central nervous system disease is critical to accurately identify candidates for central nervous system prophylaxis vs. therapy. [3][4][5] This report by the Spanish Lymphoma Group (GELTAMO) aims to provide useful guidelines and recommendations for the prevention, diagnosis, and treatment of central nervous system diffuse large B-cell lymphoma patients with, or at risk of, leptomeningeal and/or brain parenchyma lymphoma relapse. A panel of lymphoma experts working on behalf of GELTAMO reviewed all data published on these topics available in PubMed up to May 2016. Recommendations were classified according to the Grading of Recommendations Assessment Development and Evaluation (GRADE) approach. 6 A practical algorithm based on the proposed recommendations was then developed (Figure 1 have concluded that the incidence of CNS relapse decreased after the introduction of rituximab (Table 1). The identification of risk factors has been the major goal of many studies of CNS involvement. Several large retrospective studies conducted in the pre-rituximab era [12][13][14][15] reported higher rates of CNS relapse in patients with increased serum lactate dehydrogenase (LDH) levels and/or involvement of >1 extranodal site, although these factors failed to predict CNS relapse in more than half of all cases.12 In addition to the involvement of >1 extranodal site and increased LDH, International Prognostic Index (IPI) score was also identified as an independent predictor for CNS relapse in other studies.13,16 A post-rituximab era study of 399 DLBCL patients, randomized to R-CHOP or CHOP chemotherapy, 3 identified an age-adjusted IPI (aaIPI) >1 as the only risk factor for CNS involvement, although a high aaIPI score was recorded for more than 60% of the patients. When aaIPI was excluded from the analysis, elevated LDH and a poor performance status (PS >1) were identified as independent predictive factors for CNS relapse. Similarly, in the randomized RICOVER-60 trial, 4 the combination of increased LDH levels, the involvement of >1 ex...