High sensitivity of flow cytometry improves detection of occult leptomeningeal disease in acute lymphoblastic leukemia and lymphoblastic lymphoma

Conventional cytology (CC) of cerebrospinal fluid (CSF) fails to demonstrate malignant cells in up to 45 % of patients with acute lymphoblastic leukemia or lymphoblastic lymphoma (ALL/LL) in whom occult leptomeningeal disease is present. Flow cytometry (FCM) is considered more sensitive than CC, but clinical implications of CC negativity/CC positivity are not yet established. CSF samples from 38 adult patients with newly diagnosed ALL/LL were examined. Five (13 %) and nine (24 %) specimens were CC positive-FC positive (FCM^pos/CC^pos) and CC negative-FC positive (CC^neg/FCM^pos), respectively. The remaining 24 (63 %) samples were double negative (CC^neg/FCM^neg) (p = 0.001). CC^neg/FCM^pos patients showed a significantly shorter overall survival (OS) compared to CC^neg/FCM^neg ones. In multivariate analysis, the status of single FCM positivity was demonstrated to affect independently duration of OS (p = 0.005). In conclusion, FCM significantly improves detection of leptomeningeal occult localization in ALL/LL and appears to anticipate an adverse outcome. Further prospective studies on larger series are needed to confirm this preliminary observation.