S4662 A Rare Case of Gastric Myeloid Sarcoma in Relapsed Acute Myeloid Leukemia

Introduction: Myeloid sarcoma is a rare extramedullary manifestation of acute myeloid leukemia (AML). Gastrointestinal occurrence is exceedingly rare. We present the case of a 49-year-old man whose workup for melena and fatigue lead to a diagnosis of gastric myeloid sarcoma in the setting of relapsed AML. Case Description/Methods: A 49-year-old man with a history of AML previously treated with chemotherapy and allogenic stem cell transplant was admitted to our hospital for melena and fatigue. Digital rectal exam deferred due to neutropenia. Labs demonstrated pancytopenia, with a hemoglobin of 5.9 g/dL. Esophagogastroduodenoscopy (EGD) was performed which revealed moderate localized gastritis in the gastric cardia and a nodular, spontaneously bleeding mass within the fundus. Biopsies were obtained and sent for pathological analysis. Subsequently, computed tomography of the abdomen and pelvis with contrast revealed asymmetric wall thickening in the fundus of the stomach suspicious for an underlying neoplasm versus gastritis. Microscopic examination of gastric biopsy specimens revealed diffuse proliferation of medium-sized mononuclear cells with nuclear irregularities and small nucleoli. Immunohistochemical analysis demonstrated atypical cells that were positive for CD34, CD43, CD68, and CD117 and negative for CD3, CD5, CD10, and CD20. These findings confirmed the diagnosis of gastric myeloid sarcoma. Discussion: Myeloid sarcoma is a rare extramedullary tumor composed of immature myeloid cells that occurs in roughly 10%-17% of AML cases. It can arise either with or without coexisting bone marrow involvement by AML. In most cases, it localizes in the skin, lymph nodes, bones, and soft tissues. The incidence of gastrointestinal involvement is extremely low with very few cases reported in medical literature. Of these cases, gastric involvement is even less frequently reported. In such cases, the presentation of nonspecific symptoms that mimic more common gastrointestinal ailments can make the diagnosis challenging. Endoscopically, it can resemble nodular gastritis, as in our patient. Considering how rare it is, immunohistochemical analysis is crucial in establishing the diagnosis. This case highlights the importance of combining clinical context, endoscopic evaluation, and pathological data to identify a rare diagnosis.