S3813 Beyond the Bone Marrow: Anorectal Granulocytic Sarcoma Presenting as GI Bleeding

Introduction: Granulocytic sarcoma is a rare extramedullary manifestation of acute myeloid leukemia (AML), seen in 2%–7% of cases. Gastrointestinal (GI) involvement is uncommon and typically affects the small bowel. Distal GI involvement, including the anorectum, is exceedingly rare. We present a case of a 63-year-old man with rectal pain and bleeding as the initial presentation of AML due to anorectal granulocytic sarcoma. Case Description/Methods: A 63-year-old man presented to the emergency department (Emergency Department) with dizziness, fatigue, rectal pain, and bleeding. He recently returned from out-of-state travel and had previously sought care for a near-syncopal episode. At that visit, labs showed leukocytosis, anemia, and thrombocytopenia. He received a transfusion and was discharged with outpatient hematology-oncology follow-up for presumed leukemia but deferred further workup until returning home. His symptoms worsened, and he returned to the Emergency Department after returning home. On arrival he was tachycardic and diaphoretic. Labs showed white blood cell count of 23.7 K/μL, hemoglobin 7.4 g/dL, and platelets 54 × 10⁹/L. Computed tomography (CT) angiography revealed no active GI bleeding but showed circumferential thickening at the anorectal junction and sclerotic bone lesions. He was admitted for further evaluation of suspected AML. Bone marrow biopsy was positive for AML. Gastroenterology was consulted for rectal pain and concerning imaging findings. Due to severe pain, digital rectal exam was deferred. Flexible sigmoidoscopy revealed an ulcerated anorectal mass with surrounding induration. Cold forceps biopsies showed ulcerated mucosa with granulation tissue and rare, atypical blasts, consistent with circulating leukemia cells. The findings, combined with imaging and new AML diagnosis, supported a diagnosis of anorectal granulocytic sarcoma. He was started on 7 + 3 induction chemotherapy but developed atrial fibrillation with rapid ventricular response and worsening respiratory distress. He was transferred to the ICU and later opted for hospice care. He passed peacefully 2 days later. Discussion: This case highlights the rarity and aggressiveness of anorectal granulocytic sarcoma, with only 4 prior reported cases. Prognosis is poor, with median survival around 9 months. While often associated with relapse in known leukemia, it can rarely present as the initial sign, as in this case. Early recognition is essential when unexplained GI symptoms occur alongside cytopenias or concern for hematologic malignancies.