Revision of staging system for natural killer T-cell lymphoma: A multicenter study from the Chinese Southwest Oncology Group and Asia Lymphoma Study Group.

7001 Background: Natural killer T-cell lymphoma (NKTCL), characterized by extranodal involvement, challenges the efficacy of the Ann-Arbor staging system (AASS) in its precise prognostic stratification. A revised staging system is warranted for precise prognosis prediction in the modern chemotherapy era. Methods: A training cohort of patients with newly diagnosed NKTCL was assessed to revise the AASS in the context of the modern chemotherapy era. The results were validated in an independent international cohort that received asparaginase-based chemotherapy. Results: Our analysis of 2017 newly diagnosed NKTCL patients from 19 centers across two countries highlights the limitations of the AASS, which demonstrates an uneven patient distribution and insufficient differentiation of outcomes, particularly between stages III and IV. We proposed a revised staging system in which AASS stage I patients with nasal-type disease only were classified as stage I, whereas those with local invasion or limited non-nasal-type disease were reclassified as stage II. AASS stage II patients with regional lymph node involvement were assigned to stage III. Additionally, patients with distant lymph node involvement or extensive skin/subcutaneous soft tissue involvement were classified as stage IVA, those with extensive visceral organ invasion were classified as stage IVB, and those with bone marrow infiltration or hemophagocytic lymphohistiocytosis were classified as stage IVC. This proposal better distinguishes clinical outcomes across different stages, achieves a more equitable distribution of patients, and demonstrates multiple advancements over the AASS. Conclusions: The revised staging system is promising for the staging of NKTCL patients with different prognoses and could be useful for decisions regarding the treatment strategy and future clinical trial designs.