Primary and secondary central nervous system mature T- and NK-cell lymphomas

Primary central nervous system (CNS) mature T- and NK-cell lymphomas are rare, only comprising 2% to 3% of all primary CNS lymphomas. Among them, peripheral T-cell lymphoma, not otherwise specified, anaplastic large cell lymphoma (ALCL), and extranodal NK/T-cell lymphoma (ENKTL) are the commonly reported histological subtypes. Secondary CNS T-cell lymphoma generally affects about 5% of patients with T- or NK-cell lymphoma, with some exceptions. Acute and lymphomatous subtypes of adult T-cell leukemia/lymphoma (ATLL) have high risk of CNS progression, may affect up to 20% of patients; ALK-positive ALCL with extranodal involvement >1 also has high risk of CNS progression. However, the impact and the optimal methodology of CNS prophylaxis remain unclear in systemic T-cell lymphomas. There are little data on the treatment strategy of primary and secondary CNS T-cell lymphoma. Treatment strategy derived from B-cell CNS primary lymphoma is generally used; this includes induction therapy with high-dose methotrexate-based regimens, followed by high-dose chemotherapy with autologous stem cell transplant in fit patients. There are unmet needs for patients who are not fit for intensive chemotherapy. The prognosis after CNS progression in T-cell lymphoma is dismal with the median overall survival of less than 1 year. New agents targeting T-cell lymphomas are emerging and should be tested in patients with mature T- and NK-cell lymphoma who suffer from CNS involvement.