S5201 A Case of Extramedullary Plasmacytoma Involving the Pancreas

Introduction: Extramedullary plasmacytomas (EMPs) are rare plasma cell tumors arising outside bone marrow (∼3% of plasma cell disorders). Pancreatic involvement (<5% of EMPs) mimics pancreatic adenocarcinoma clinically and radiologically. Accurate differentiation is crucial due to significant treatment and prognosis differences. This case highlights pancreatic EMP in a multiple myeloma patient, emphasizing the need for careful evaluation and diagnosis. Case Description: A 77-year-old woman with hypertension, hyperlipidemia, hypothyroidism, anemia, melanoma, and untreated extramedullary plasmacytoma was evaluated for a pancreatic head mass noted on imaging. Initially presenting with a left breast mass, her exam also revealed pedal edema. Labs showed hemoglobin 11.1 g/dL, hematocrit 33.3%, red blood cell count 3.48 × 10⁶/µL, and elevated MCV (95.7 fL). Mammography identified an oval breast mass, with ultrasound showing suspicious solid lesions. Breast biopsy confirmed a plasma cell neoplasm (CD38/CD138-positive, kappa light chain-restricted). Further labs revealed an elevated kappa-lambda ratio (4.21) and high kappa free light chains (26.34 mg/L). Bone marrow had 12% plasma cells. Positron emission tomography imaging detected lesions in the forehead, pancreatic head, costovertebral joint, abdominal wall, and diffuse marrow uptake. Magnetic resonance cholangiopancreatography characterized an 11 mm hyperenhancing pancreatic head lesion. Forehead biopsy indicated aggressive kappa-clonal plasma cells (Ki67 >90%). Bone marrow biopsy showed 25% kappa-restricted plasma cells, confirming multiple myeloma. Fluorescence in situ hybridization revealed high-risk cytogenetics (gain 1q, loss 1p, monosomy 13, partial 5’IGH deletion, loss 16q). EUS showed a 12 mm × 15 mm hypoechoic pancreatic mass. Fine-needle biopsy confirmed plasmacytoma (50% cellularity, CD138-positive, IgG-positive, Ki67 proliferation 50%). The patient began systemic treatment with daratumumab, lenalidomide, aspirin, acyclovir, and dexamethasone. Discussion: EMP of the pancreas is rare and often appears similar to pancreatic adenocarcinoma, typically causing jaundice and abdominal pain. Most commonly found in the head of the pancreas, EMPs occur more frequently in patients with multiple myeloma and usually indicate aggressive underlying disease. Fortunately, EMPs tend to have a better prognosis than pancreatic adenocarcinoma, highlighting the importance of timely biopsy and immunohistochemistry. Early and accurate diagnosis can lead to more effective treatment, reducing unnecessary surgeries and significantly improving outcomes.