S4826 An Unusual Cause of Rectal Bleeding: Rectal Mass From Abnormal Extramedullary Hematopoiesis in the Setting of Chronic Myelomonocytic Leukemia

Introduction: A rectal mass causing rectal bleeding is most commonly rectal adenocarcinoma, though other malignancies and benign lesions are also in the differential diagnosis. Extramedullary hematopoiesis is rarely found in the gastrointestinal (GI) luminal tract and has not previously been reported as a cause of lower GI bleeding. We report a case of a rectal bleeding from a rectal mass due to extramedullary hematopoiesis in the setting of chronic myelomonocytic leukemia 1 (CMML-1). Case Description/Methods: A 67-year-old man with CMML-1 managed with supportive care and high-risk stage IIC prostate cancer status post external beam radiation therapy, presented to the Emergency Department with rectal bleeding. His initial lab results showed a hemoglobin of 11.4 gm/dL, white blood cell count of 47.7 k/cm2, and platelet count of 48 k/cm2. Computed tomography abdomen pelvis revealed splenomegaly and thickening of the inferior rectum with presacral fat stranding. Of note, 6 months prior, he presented with rectal bleeding and underwent colonoscopy that showed localized angiodysplastic lesions with bleeding on contact in the mid-rectum, consistent with radiation proctitis, that were successfully treated with coagulation for tissue destruction using argon plasma. On this presentation, he was admitted and underwent repeat colonoscopy that showed a villous, fungating, polypoid mass in the rectum. The mass was oozing and partially circumferential, measuring twenty millimeters in length and twenty-5 millimeters in diameter. Biopsy demonstrated a diffuse mixed cellular infiltrate composed of maturing granulocytic cells, erythroid precursors, and megakaryocytes. The infiltrate showed granulocytic predominance with left shift and scattered aggregates of immature mononuclear cells. Necrotic rectal mucosa, fibrosis, and hemorrhage were present in the background, consistent with infarct changes. Stains were consistent with abnormal extramedullary hematopoiesis in the setting of CMML. A repeat bone marrow biopsy confirmed persistent CMML-1 with 3% blasts. The patient was treated with 5 cycles of decitabine for CMML-1 resulting in complete resolution of rectal bleeding. Discussion: Rectal mass biopsy in this patient showed a previously undescribed cause of rectal mass – extramedullary hematopoiesis. This case highlights an unusual cause for lower GI bleeding, but one that is important to consider in patients with myeloproliferative or myelodysplastic disorders.