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Extranodal natural killer (NK)/T-cell lymphoma (ENKTL) is a rare subtype of non-Hodgkin lymphoma (NHL) with poor prognosis, particularly in relapsed or refractory patients. Thus, timely detection of relapse and appropriate disease management are crucial. We present two patients with ENKTL, wherein positron emission tomography-computed tomography (PET-CT) with total-body coverage after induction therapy, detected newly relapsed regions in the bone marrow of the lower leg prior to progression. Case 1: A 47-year-old woman with nasal obstruction, showing 18F-fluoro-deoxyglucose (FDG) uptake in the nasal cavity (Lugano stage IE). After induction therapy (RT-2/3 DeVIC), PET-CT revealed abnormal uptake only in the right fibula. Case 2: A 68-year-old man with a skin nodule/ulcer and an enlarged right inguinal lymph node was diagnosed with advanced ENKTL. A PET-CT scan revealed abnormal uptake in the subcutaneous mass of the right medial thigh, lymph nodes, and descending colon (Lugano stage IV). After induction therapy, PET-CT revealed new abnormal uptake only in the left tibia. In both patients, CT-guided biopsy confirmed ENKTL recurrence. Moreover, PET-CT with whole-body coverage was useful for the timely assessment of relapse and detection of asymptomatic bone involvement. This approach allowed for modifications to treatment strategies in certain patients.

Follicular T-cell lymphoma (FTCL) is a rare disease, recently defined in the revised WHO classification Tumours of Haematopoietic and lymphoid tissues (4th edition). Although angioimmunoblastic T-cell lymphoma (AITL) and FTCL share similar T follicular helper (TFH) cell immunophenotypes and gene mutations, the clinical course of FTCL is not well characterized. Herein, we report the case of a 91-year-old woman with FTCL, who was successfully treated with corticosteroid. The patient, who had systemic lymphadenopathy and splenomegaly, was first diagnosed with necrotizing lymphadenitis. Re-biopsy was performed because of her persistent lymphadenopathy, which revealed FTCL. She was treated with corticosteroid because of her advanced age, poor performance, edema, and pleural effusion. After administering 100 mg prednisone, her condition improved and was discharged with prednisone tapering. Six-month positron emission tomography-computed tomography (PET-CT) scan showed complete metabolic remission. With a low dose of prednisone (6-10 mg), she remained disease-free for >3 years. Thus, these findings suggest that corticosteroid treatment is effective in some patients with peripheral T-cell lymphoma of TFH origin, including FTCL.