1621 Extramedullary Plasmacytoma of the Colon

INTRODUCTION: Plasma cell tumors can be categorized into multiple myeloma or plasmacytomas. Plasmacytoma is the proliferation of neoplastic monoclonal plasma cells in sites other than the bone marrow. This case illustrates a rare case of plasmacytoma in the colon. CASE DESCRIPTION/METHODS: A 49-year-old man with medical history of type 1 DM and GERD presented for average risk screening colonoscopy. Colonoscopy showed a 12mm transverse colon polyp that was resected via hot snare polypectomy. Pathology of the 12mm polyp showed lamina propria expansion with large sheets of plasma cells. On immunohistochemistry (IHC), the plasma cells showed kappa light chain restriction. IHC gene rearrangement studies showed a low level of immunoglobulin heavy chain amplification. Pathology was consistent with plasmacytoma associated with tubular adenoma without high grade dysplasia. Margins were negative. A complete blood count obtained by primary care physician demonstrated Hgb of 14.1 g/dl. Complete metabolic panel was normal. Serum protein electrophoresis, urine Bence Jones protein, bone marrow biopsy, skeletal bone survey and PET CT scan were recommended to exclude multiple myeloma and involvement at other sites. DISCUSSION: Plasmacytoma can be either be solitary bone plasmacytoma or solitary extramedullary plasmacytoma. The diagnosis of solitary plasmacytoma depends on the exclusion of multiple myeloma via normal bone marrow biopsy, normal skeletal survey and absence of end organ damage. If multiple myeloma is present, the lesion is characterized as an extramedullary manifestation of multiple myeloma. Solitary bone plasmacytoma occurs most commonly in the vertebrae. Solitary extramedullary plasmacytoma involves sites other than bone or bone marrow. It most commonly involves the nasopharynx or upper respiratory tract and is observed in 3-5% of plasma cell tumors. Colonic extramedullary plasmacytoma is rare and occurs in approximately 10% of extramedullary cases. Clinical presentations of extramedullary plasmacytoma are variable and depend on site of involvement. There are no current guidelines for the treatment of patients with colonic plasmacytoma. It is unclear whether endoscopic or surgical resection alone suffices as conclusive management or additional treatment modalities like radiotherapy or chemotherapy is necessary.