Secondary Extramedullary Plasmacytoma of the Stomach: A Rare Manifestation of Relapsed Multiple Myeloma

Introduction/Background/Significance: Plasma cell tumors include solitary plasmacytomas and multiple myeloma (MM). Extramedullary plasmacytomas (EMP) are rare soft tissue manifestations of plasma cell neoplasms. Secondary EMP, typically associated with relapsed or refractory MM, results from marrow-independent plasma cell migration and is associated with poor prognosis [1,2]. Gastrointestinal (GI) involvement occurs in only 0.9% of MM cases [3]. This case highlights a rare gastric relapse of MM following autologous bone marrow transplant.

Materials and Methods/Case Presentation/Objective: A 64-year-old female presented with a 3-month history of intermittent abdominal pain, nausea, vomiting, and a 20-pound unintentional weight loss. Laboratory evaluation revealed normocytic anemia (Hb 7.4), hypercalcemia, hyperphosphatemia, and elevated total protein (11.9 g/dL). Bone marrow biopsy showed >90% plasma cells, with flow cytometry confirming 70% monoclonal IgG kappa plasma cells. FISH revealed trisomy 7, 9, 15 and monosomy 13. She was diagnosed with MM complicated by renal failure requiring dialysis and initiated on a CyBorD regimen with acyclovir prophylaxis and denosumab.

Six months after the diagnosis, she underwent autologous stem cell transplant. Post-transplant evaluations showed no evidence of recurrence. However, four months after transplantation, she was re-admitted with melena and anemia. EGD revealed a 10 mm gastric submucosal nodule; biopsy confirmed gastric plasmacytoma with monoclonal IgG kappa cells (0.7%). Repeat bone marrow biopsy showed normocellular marrow with < 3% plasma cells, consistent with secondary EMP relapse. She was treated with IV dexamethasone, PPI drip, pamidronate, and calcitonin. Radiation was given to the gastric lesion, and a daratumumab-based chemotherapy regimen (D-VRd) was planned. The patient expired 2 weeks after starting the chemotherapy regimen due to complications of the disease.

Results/Description/Main Outcome Measures: This case highlights a rare and aggressive manifestation of MM relapse as secondary EMP of the stomach. Our patient, who initially responded well to induction therapy and autologous stem cell transplantation, experienced a gastric relapse within four months despite showing no evidence of marrow involvement post-transplant. This underscores the unpredictable nature of extramedullary disease (EMD) and the importance of maintaining a high index of suspicion in patients presenting with atypical gastrointestinal (GI) symptoms—even in the absence of significant bone marrow plasma cell infiltration.

Gastric EMPs are exceptionally rare and often present with non-specific GI symptoms such as bleeding or abdominal discomfort, as seen in our patient. Endoscopic biopsy remains the gold standard for diagnosis, while PET/CT imaging is essential for comprehensive disease assessment.

Treatment of secondary EMP requires systemic therapy. While our patient was started on a daratumumab-based regimen (D-VRd), the disease course was rapidly progressive, consistent with literature showing poor outcomes and short-lived responses in extramedullary relapse. Radiation was used for local control of the gastric lesion, but her clinical status deteriorated quickly.

Conclusions: This case emphasizes the aggressive behavior and poor prognosis associated with secondary GI EMP. It highlights the need for vigilant post-transplant surveillance, particularly in high-risk patients, and calls for inclusion of such cases in prospective studies to better inform treatment strategies and improve survival outcomes.

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References

1] Alexiou C, et al. Cancer. 1999;85(11):2305-14.

[2] Usmani SZ, et al. Haematologica. 2012;97(11):1761.

[3] Talamo G, et al. Haematologica. 2006;91(7):964-967.