A Case of Pediatric Subcutaneous Panniculitis-like T-Cell Lymphoma Successfully Treated with Immunosuppressive Therapy.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a very rare subtype of cutaneous T-cell lymphoma. It is characterized by the neoplastic infiltration of subcutaneous adipose tissue. Its clinical presentation, including subcutaneous nodules, fever, and systemic symptoms, often mimics inflammatory panniculitis, making diagnosis difficult. This case report describes a 14-year-old female presenting with fever, limb pain, swelling, and subcutaneous nodules, who was ultimately diagnosed with SPTCL via punch biopsy and BIOMED-2 clonality assays, confirming positive T-cell receptor-γ chain gene rearrangement. Positron emission tomography-computed tomography revealed diffuse subcutaneous involvement across multiple body regions. Methylprednisolone and cyclosporine A treatment rapidly resolved her symptoms, with laboratory parameters, including ferritin and inflammatory markers, showing significant improvement. Next-generation sequencing identified a heterozygous C9 gene mutation (c.346C>T, p.Arg116Ter), adding a novel genetic dimension to the case. Following a tapered discontinuation of immunosuppressive therapy, the patient achieved sustained remission without relapse for over 1 year. We report a case of adolescent SPTCL treated with immunosuppressive therapy and suggest that immunosuppressive therapy should be considered before chemotherapy in pediatric patients with SPTCL but without HLH.