Pediatric T-Cell/Histiocyte-Rich Large B-Cell Lymphoma (THRLBC) in an 8-Year-Old Male Child: A Case Report

T-cell/histiocyte-rich large B-cell lymphoma (THRLBCL) is a rare and aggressive subtype of diffuse large B-cell lymphoma (DLBCL) that is uncommon in children. Here, we present the case of an 8-year-old male with a 3-month history of low-grade intermittent fever, significant weight loss, loss of appetite, and progressive abdominal swelling. Examination revealed splenomegaly and a palpable midabdominal mass, with laboratory findings showing bicytopenia. Imaging demonstrated hepatosplenomegaly, diffuse hypodense liver and spleen lesions, and mesenteric and retroperitoneal lymphadenopathy. A core-needle biopsy of the mesenteric mass confirmed the diagnosis, with histopathology revealing scattered large mononuclear and binucleate cells in a background of small lymphocytes and histiocytes. Immunohistochemistry showed positivity for CD45, CD20, and EMA and negativity for CD30, CD15, and Bcl-2, excluding alternative diagnoses such as nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) and classical Hodgkin lymphoma (cHL). The patient was initially stabilized with a prephase regimen of cyclophosphamide, vincristine, and prednisone (COP), followed by induction and consolidation with R-COPADM (rituximab, cyclophosphamide, vincristine, prednisone, and methotrexate). Posttreatment imaging revealed significant resolution of lymphadenopathy and hepatosplenomegaly, with no residual or recurrent disease. At follow-up, the patient remains in clinical remission with no signs of progression. This case highlights the importance of early recognition, detailed histopathological evaluation, and the role of immunohistochemistry in accurately diagnosing THRLBCL in children, ensuring timely initiation of effective therapy and improving outcomes in this rare pediatric malignancy.