Non-deep-seated primary CNS lymphoma: therapeutic responses and a molecular signature

The survival of patients with primary CNS lymphoma (PCNSL) has been improved by high-dose methotrexate (HD-MTX). Since the combination therapy of HD-MTX and whole-brain radiotherapy (WBRT) carries a significant risk for delayed neurotoxicity, it is important to know the therapeutic potential and prognostic factors for HD-MTX without WBRT. We retrospectively reviewed 46 consecutive patients with PCNSL treated with a HD-MTX (3.5 g/m²) and deferred WBRT. Patients who achieved complete response or partial response after three courses of HD-MTX were cautiously followed-up without additional treatment. Patients who had either stable disease, progressive disease, or disease relapse were offered salvage therapy. The median progression-free survival period was 10 months and the median overall survival period was 52 months, with a 5-year survival rate of 39 %. Nineteen patients (49 % of the evaluable patients) achieved a complete response at the initial response assessment. Involvement of deep structures of the brain (corpus callosum, basal ganglia and brainstem) was significantly associated with the worse progression-free survivals (p = 0.0058) and overall survivals (p = 0.0177). Gene expression profiling analysis by microarray was compared in eight patients between PCNSLs located in the deep structures of the brain and non-deep-seated tumors. The result showed that up-regulation of signal transduction-related genes and down-regulation of catalytic activity-related genes in the non-deep-seated PCNSL compared with the deep-seated tumors. The present study shows that PCNSL located in non-deep structures of the brain responds better to HD-MTX alone than those involved deep-structures.