Germinal center B-cell diffuse large B-cell lymphoma presenting as a chin mass: a case report.

Introduction and importance: Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma, often presenting with nodal or extranodal masses. However, involvement of the chin region is extremely rare and underreported in literature. This case highlights an unusual extranodal manifestation of germinal center B-cell-like (GCB) DLBCL. Case presentation: A 56-year-old man with a history of hypertension and type II diabetes presented with an 8-month history of a painless, progressively enlarging chin mass. Prior antibiotic therapy failed to resolve the lesion. Examination revealed a firm, 4 × 3 cm subcutaneous swelling involving skin and mucosa. Computed tomography (CT) and positron emission tomography/CT imaging revealed hypermetabolic soft tissue lesions in the chin and right buccogingival region. Histopathology and immunohistochemistry confirmed GCB-type DLBCL. The patient received six cycles of rituximab, cyclophosphamide, pirarubicin, vincristine, and prednisolone chemotherapy, resulting in a significant reduction in lesion size and metabolic activity. Follow-up showed no recurrence. Clinical discussion: This case highlights the diagnostic challenges posed by extranodal DLBCL in atypical locations. Misdiagnosis as an infection led to a delayed diagnosis. Immunophenotyping revealed expression of both B- and T-cell markers, which complicated the classification of the lymphoma. A prior history of spontaneously resolving axillary masses suggested an indolent precursor phase that later transformed into aggressive DLBCL. Conclusion: DLBCL may present in rare extranodal sites such as the chin, mimicking benign conditions. Persistent lesions unresponsive to antibiotics should prompt a malignancy workup. Comprehensive evaluation, including imaging and immunohistochemistry, is critical for timely diagnosis and effective treatment. Further research is needed to understand unusual immunophenotypes and progression pathways in DLBCL.