Risk Stratification of Nodal PTCL

Inclusion Criteria: * Patients diagnosed with nodal PTCLs (PTCL, NOS; Angioimmunblastic T-cell lymphoma; anaplastic large cell lymphoma \[ALCL\], anaplastic lymphoma kinase \[ALK\]-negative) * Patients diagnosed with between January 1, 2004 and April 30, 2016 * initially treated with curative intent * Patients with standard 18F-fluorodeoxyglucose (FDG) PET or PET-CT data at the time of diagnosis and at the end of primary treatment Exclusion Criteria: * Patients diagnosed with extranodal PTCLs, including followings (extranodal NK/T-cell lymphoma, nasal type; enteropathy-associated T-cell lymphoma; hepatosplenic T-cell lymphoma; subcutaneous panniculitis-like T-cell lymphoma; EBV-positive T-cell lymphoproliferative childhood disorders, and primary cutaneous lymphomas) * Patients with ALCL-ALK+ * Patients who do not have 18F-FDG PET or PET-CT data either at diagnosis or at the end of treatment available for review