Clinical relevance of flow cytometric immunophenotyping of the cerebrospinal fluid in patients with diffuse large B-cell lymphoma

Central nervous system (CNS) relapse is an uncommon but dramatic complication of diffuse large B-cell lymphoma (DLBCL). Several studies have demonstrated the superiority of cerebrospinal fluid (CSF) flow cytometry (FCM), as compared with conventional cytology (CC), in detecting occult leptomeningeal disease. The clinical relevance of a positive FCM still has to be clarified. We analyzed CSF from 114 DLBCL patients at diagnosis (n = 95) or at relapse (n = 19) by FCM and CC. Most patients received meningeal prophylaxis. FCM results did not influence treatment strategies. Fourteen samples were FCM+, versus one CC+ (also FCM+). Within all patients without neurological symptoms (n = 101), four (4%) relapsed in the CNS, with a median time to relapse of 5.2 months. Only one-fourth (25%) was FCM+ before relapse. More than one extranodal disease site and elevated lactate dehydrogenase levels were associated with an increased risk of CNS relapse. FCM gives far more positive results than CC. However, a positive FCM result did not translate into a significant increase in CNS relapse rate in this histologically uniform population receiving CNS prophylaxis.