Clinical Course of Adult T-Cell Leukemia-Lymphoma with Central Nervous System Involvement

Background: Adult T-cell leukemia-lymphoma (ATL) is a peripheral T-cell lymphoma with a highly diverse clinical presentation. Although central nervous system (CNS) involvement is common, the detailed clinical presentation of CNS-ATL needs to be clarified. Objective: This study aims to clarify the clinical course of ATL with CNS involvement. CNS involvement was classified according to the criteria of JALSG202 for acute lymphocytic leukemia as follows: Grade I: no symptoms and cerebrospinal fluid (CSF)cell count less than 5/μl and presence of abnormal lymphocytes; Grade II: asymptomatic and CSF cell count 5-50/μl and presence of abnormal lymphocytes; Grade III: symptomatic or CSF cell counts > 50 cells/μl and presence of abnormal lymphocytes. Results: The analysis included 213 cases of ATL treated at Kagoshima University Hospital from 2002 to 2021. Of these aggressive ATL cases, the clinical subtypes at initial presentation were as follows: acute type 109, lymphoma type 54, chronic type 30, smoldering type 18, and 2 cases were unclassifiable. The median age of the patients was 63 years, and 96 cases (45.1%) were women. Sixty patients had received allogeneic hematopoietic stem cell transplants. During the clinical course, 28 patients (13.1%) with a median age of 61 years and 13 women（46.4%）had CNS involvement. Two cases were classified as Grade I, six as Grade II, and 20 as Grade III. Among them, nine patients (4.2%) showed neurological symptoms at the initial ATL diagnosis, and 1 patient presented with neurological findings at the time of chronic to acute transformation. Of the remaining 203 patients, prophylactic intrathecal chemotherapy was administered in 101 cases, at which time CNS involvement was diagnosed in 9 cases (8.9%). Three patients developed symptomatic involvement while responding to chemotherapy. One patient developed symptomatic involvement when refractory to chemotherapy. Four cases were CNS recurrence with systemic disease progression after remission. Two cases were identified as primary CNS-ATL. The simplified ATL-PI (Prognostic Index) at initial ATL diagnosis for the 28 patients with CNS involvement revealed four cases with high-risk, thirteen with intermediate-risk, two with low-risk, six not eligible due to indolent ATL subtypes, and three cases with unknown risk. The incidence of CNS involvement by ATL subtype was 17.8% (19/107) for acute type, 1.8% (1/54) for lymphoma type, 16.7% (5/30) for chronic type, and 0% for smoldering type (excluding 1 case of unknown subtype and 2 cases of primary CNS-ATL) at ATL diagnosis. At the diagnosis of CNS involvement, 15 (53.6％) patients showed at least 5% of ATL cells in the peripheral blood. During a median observation period of 429 days, the 1-year cumulative incidence of CNS involvement was 12.3% (95% CI 8.3-17.1%). High-dose methotrexate-based therapy was administered to 5 patients with CNS involvement, which had a certain effect on CNS lesions but had limited efficacy for other lesions. All of these cases were treated with concomitant intrathecal chemotherapy. The 2-year overall survival rate after diagnosis of CNS involvement was 16.9% (95% CI 4.9-35.2%). The CNS-IPI (International Prognostic Index) did not predict CNS involvement in ATL. Conclusions: This is the largest study to examine the clinical course of CNS involvement of ATL. The 1-year cumulative incidence of CNS involvement was 12.3%, indicating that CNS involvement is an early complication after diagnosis of aggressive ATL, especially in leukemic subtypes. The prognosis after the diagnosis of CNS involvement was also clarified. The high frequency of CNS involvement during prophylactic intrathecal chemotherapy in patients with ATL without neurological symptoms suggests that it is an important clinical question that needs to be addressed.