Unusual Lymphoma Found on Routine Colonoscopy—Whatʼs Hiding in Your Colon?

Abstract

Introduction: Primary malignant lymphoma of the large intestine is a rare condition, accounting for only 0.2% of primary neoplasms of the large intestine. Furthermore, intestinal extranodal marginal zone B-Cell lymphoma (MZL) of mucosa-associated lymphoid tissue (MALT) type is extremely rare. We present a case of MALT lymphoma involving only the colon. Case Report: A 57 year old female presented to her primary care physician's office for a routine health exam. Review of systems was negative for weight loss, fatigue, fevers, chills and night sweats. The patient denied any hematochezia or alteration in bowel function. Physical exam was remarkable for a rectal polyp palpatable on digital rectal exam. Stool was hemoccult negative. Laboratory studies revealed normal CBC, creatinine, calcium and hepatic function. Patient underwent colonoscopy which revealed a five mm rectal polyp and a 4 cm frond-like villous mass at 60cm. The rectal polyp was hyperplastic. The mass histologically demonstrated lymphoma features and subsequent hemicolectomy was performed. Surgical specimen was consistent with extranodal marginal zone B-cell lymphoma of MALT type. Discussion: MZL accounts for approximately 8% of all NHL. The stomach is the most common site of MZL of MALT type. The ileum is the most common small bowel site. MALT lymphomas, when found in the large bowel, most commonly effect the rectum. Clinically, MALT lymphoma is typically indolent, remaining localized for prolonged periods. When found, it usually requires surgical excision and current conjunctive chemotherapy (Rituximab). Histologically, MALT is characterized by lymphoepithelial lesions and reactive lymphoid follicles. It is important to histologically distinguish between MALT lymphoma and mantle cell lymphoma because the latter carries poor prognosis. Unlike mantle cell, MALT lymphomas are negative for CD1 and CD5 tumor markers. This case represents an unusual finding on a routine screening colonoscopy in an asymptomatic patient. In addition, our patient is unique in that she does not have evidence of NHL in the presence of an isolated colonic MZL of MALT type. She continues to do well after resection and is receiving conjunctive chemotherapy.