Sigmoid Plasmacytoma Mimicking Colon Cancer in a Multiple Myeloma Patient

Abstract

Purpose: Colonic plasmacytomas are a rare manifestation of a myeloma malignancy, with less than 25 cases reported. We report such a case occurring in the sigmoid colon with the symptoms mimicking colon cancer and review the literature. Awareness of this complication in patients with multiple myeloma is important to provide early diagnosis and treatment. A 52-year-old man presented to the emergency room with intermittent hematochezia for several weeks. He was diagnosed with multiple myeloma two years previously and had been treated with chemotherapy and bone marrow transplantation. The initial response to treatment was favorable, and his disease was in remission at the time of presentation. There was no family history of colorectal cancer and no previous screening colonoscopy. He denied alcohol ingestion, non-steroidal anti-inflammatory drug use, and smoking. His vital signs were normal. Initial hematocrit was 21.7% and he received blood transfusions. Two days after admission, colonoscopy revealed a large fungating, partially obstructing mass in the lower sigmoid colon (Figure A); the remainder of the colon was normal. Biopsied specimens from the mass lesion were consistent with plasmacy-toma, and immunohistochemical stains showed strong expression of CD138 and CD79a by the neoplastic cells (Figure B). At exploratory laparotomy, the mass was large and extended into the sigmoid mesentery, anterior rectum and bladder. Surgical resection included the sigmoid colon, upper rectum, and a portion of the posterior superior bladder. On histologic examination, the 12 cm diameter plasmacytoma invaded through the wall of the colon into the pericolonic fat; seven lymph nodes were all negative. The patient recovered uneventfully and further chemotherapy was planned as an outpatient. Extra-medullary colonic plasmacytoma is a rare manifestation of multiple myeloma. It has many different presentations, including rectal bleeding or bowel obstruction. The endoscopic appearance has no characteristic features to differentiate it from other tumors, and thus biopsy is essential. Though there are no defined treatment guidelines, surgical resection and chemotherapy have been used for localized colonic presentations. Manifestation of these symptoms in myeloma patients should prompt early colonoscopies for effective and early diagnosis and treatment.Figure A: Mass in sigmoid colon seen by colonoscopy. Figure B. Multiple plasmacytoma cells on sigmoid mass biopsy expressing CD138 (H&E, original magnification x40).