Solitary extramedullary plasmacytoma of the tongue: a case report

Introduction and Importance: Extramedullary plasmacytomas are rare solitary plasma cell neoplasms that occur outside the bone marrow. Primary tongue involvement is exceptionally uncommon and presents a significant diagnostic challenge. Their clinical presentation is often subtle and may closely mimic more common neoplastic processes. Case Presentation: We report the case of a 35-year-old man who presented with a gradually enlarging, firm, and painless mass on the ventral surface of the tongue that had been evolving for 5 months. Histopathological and immunohistochemical analyses revealed sheets of atypical plasma cells expressing CD38 and CD138 with kappa light-chain restriction, consistent with monoclonal plasma cell proliferation. A comprehensive systemic evaluation excluded multiple myeloma. The patient underwent definitive radiotherapy with a total dose of 50 Gy delivered in 25 fractions, resulting in complete remission without any functional impairment. At 9 months of follow-up, the patient showed no evidence of local recurrence or progression to multiple myeloma. Clinical Discussion: Primary extramedullary plasmacytoma of the tongue is exceptionally rare and may clinically mimic more common malignant or benign lesions, particularly in patients with a history of tobacco and alcohol exposure. An accurate diagnosis requires a multidisciplinary approach that integrates clinical findings, imaging, and histopathology, with immunohistochemical confirmation of monoclonality. Currently, radiotherapy remains the cornerstone of treatment, providing excellent local control and durable long-term remission. Conclusion: This case underscores the exceptional rarity of primary extramedullary plasmacytoma of the tongue and highlights the effectiveness of radiotherapy as a curative and function-sparing treatment option for this condition, while emphasizing the necessity of long-term and lifelong surveillance to detect potential late recurrence or progression to multiple myeloma.