Clinical and Biological Cohort Study of EBV-Positive T/NK-Cell Lymphoproliferative Diseases

This is a multicenter, non-interventional, ambidirectional cohort study of Epstein-Barr virus-positive T/NK-cell lymphoproliferative diseases. The study consists of a retrospective clinical cohort of 500 consecutively diagnosed patients with extranodal NK/T-cell lymphoma and a prospective clinical-biological cohort of 1,000 newly diagnosed patients with extranodal NK/T-cell lymphoma, aggressive NK-cell leukemia, systemic chronic active Epstein-Barr virus disease of T/NK-cell type, or Epstein-Barr virus-positive nodal T/NK-cell lymphoma. The study will characterize clinical features, treatment pathways, response, relapse or progression patterns, and long-term survival. The prospective cohort will additionally undergo standardized collection of peripheral blood and optional tumor tissue specimens at predefined clinical time points. Clinical, molecular, viral, and immune biomarkers will be evaluated for their associations with treatment response, treatment failure, disease progression, and survival. No treatment is assigned by the study.

Inclusion Criteria: * Age 18 years or older. * Newly diagnosed Epstein-Barr virus-positive T/NK-cell lymphoproliferative disease meeting World Health Organization diagnostic criteria. * For the retrospective cohort: diagnosis of extranodal NK/T-cell lymphoma between January 1, 2017 and December 31, 2025 at a participating center. * For the prospective cohort: diagnosis between June 1, 2026 and December 31, 2030 of one of the following: * Extranodal NK/T-cell lymphoma; * Aggressive NK-cell leukemia; * Systemic chronic active Epstein-Barr virus disease of T/NK-cell type; or Epstein-Barr virus-positive nodal T/NK-cell lymphoma. * Availability of essential diagnostic, staging, and treatment information. * For the prospective cohort: written informed consent and successful collection of the protocol-required baseline peripheral blood specimen. Exclusion Criteria: * For the retrospective cohort: no usable survival follow-up information, inability to confirm survival status, or inability to calculate the principal survival outcomes. * For the prospective cohort: unwillingness or inability to participate in protocol-defined longitudinal clinical follow-up.