Extramedullary Splenic Plasmacytoma: A Rare Presentation of Multiple Myeloma

Introduction:
Multiple myeloma (MM) arises from neoplastic proliferation of plasma cells whose survival is potentiated by the bone marrow (BM) microenvironment. Extramedullary plasmacytomas (EMP) may be solitary or associated with systemic MM, can occur in nearly any organ, and are most common in the upper aerodigestive tract.(1)
Methods:
We report a case of symptomatic MM presenting with splenic EMP discovered in a patient with ipsilateral renal cell carcinoma (RCC).
Results:
A 75-year-old Caucasian male never-smoker with a history of hypertension, hyperlipidemia, and benign prostate hypertrophy presented with four-months of painless hematuria. His brother had prostate and kidney cancers, but he had no family history of hematologic malignancy. Laboratory studies showed a normal CBC and metabolic panel with a reduced creatinine clearance (CrCl) of 31 mL/min/1.73m2 (creatinine 2.0 mg/dL). CT imaging revealed two left lower pole renal masses: one 5.2 x 4.4 cm and another 3 x 2.3 cm superiorly, and in addition several splenic lesions were identified, the largest of which was 3.8 x 3.6 cm. He underwent nephrectomy showing a clear cell RCC, and splenectomy showing monoclonal plasma cells that were CD38(+),kappa(+), and CD19(-), CD20(-) CD138(-), and lambda(-), consistent with myelomatous involvement. An SPEP showed a 0.95 g/dL IgM-kappa M-spike (normal IgA and IgG), and free light chain ratio 2.96 (Kappa 101.6 mg/L). His BM biopsy was hypercellular (50-60%) with 25% CD138(+) monoclonal kappa-restricted plasma cells with normal cytogenetics. PET imaging showed non-avid subcentimeter lytic lesions in the scapulae, left 9 ribs, and right iliac bone. After diagnosis of symptomatic MM, R-ISS stage 2, he was fit to receive 4-drug induction with daratumumab, cyclophosphamide, bortezomib, dexamethasone (D-CyBorD). Following 2 cycles his CrCl improved to 58 and cyclophosphamide was replaced with lenalidomide (D-RVD) for 2 additional cycles, achieving a complete remission. He remains on DRD maintenance with monthly daratumumab and is in stringent complete remission 1 year from diagnosis.
Discussion:
To our knowledge, there are few reports of symptomatic MM presenting with splenic EMP, the majority of case having been described as solitary splenic EMP.(2) While EMP may be enriched in higher-risk patients,(3) our patient had standard risk disease. He achieved a complete response to initial treatment despite presenting with acute renal failure, which reinforces data showing high overall response rates with modern quadruplet anti-myeloma induction regimens.(4, 5) This case also highlights the variable presentation of MM and the importance of investigating suspected metastatic sites in a patient with synchronous carcinoma.