Primary Extraosseous Plasmacytoma of Pancreas: A Case Report.

Abstract

Background: Extramedullary (extraosseous) plasmacytoma is an uncommon plasma-cell neoplasm that typically arises in the upper aerodigestive tract; primary pancreatic involvement is exceptionally rare and can mimic other pancreatic head masses.

Case Report: A 55-year-old man presented with 3 months of right-sided abdominal pain, dyspnea, and pallor, with examination revealing anemia and a palpable right abdominal lump. Hemoglobin was 7.8 g/dL. Abdominal ultrasonography showed a large heterogeneous mass. ^18F-FDG PET/CT demonstrated a 6.5 × 8.3 × 10.1 cm heterogeneously enhancing lesion with internal calcifications in the pancreatic head extending to the periportal region, encasing the hepatic artery and compressing the portal vein with collateral formation, with intense FDG uptake (SUVmax 10). Endoscopic ultrasound-guided core biopsy (22G) revealed sheets of mature and atypical plasmacytoid cells, raising suspicion for a plasma-cell neoplasm. Immunohistochemistry showed tumor positivity for EMA, CD138, CD38, kappa light chain, and MUM1, and negativity for cytokeratin, lambda, CD20, CD3, synaptophysin, IgG4, EBER, and chromogranin—supporting a clonal plasma-cell process. Comprehensive evaluation for multiple myeloma (bone marrow aspiration, skeletal survey, serum/urine electrophoresis, and serum immunofixation) was negative; serum β2-microglobulin was elevated with an abnormal serum free light-chain ratio but insufficient for diagnosing systemic myeloma. A diagnosis of primary extraosseous pancreatic plasmacytoma was made. The patient received packed red blood cell transfusions and was referred for definitive external-beam radiotherapy.

Conclusion: Primary pancreatic plasmacytoma should be considered in hypermetabolic pancreatic head masses with plasmacytoid histology; EUS-guided biopsy with immunophenotypic confirmation and systematic exclusion of multiple myeloma are essential, and local radiotherapy remains the mainstay of treatment.