Colonic Myeloid Sarcoma - A Rare Presentation of Relapsed Acute Myeloid Leukemia

Abstract

A 36-year-old Caucasian female was admitted with abdominal pain and non-mucous, non-bloody diarrhea. Her medical history was significant for acute myeloid leukemia (AML) status post allogenic hematopoietic stem cell transplant 2 years ago and chronic graft versus host disease involving the skin, liver, and eyes. On admission, her hemoglobin was 7.3 g/dL and her white blood cell count was 12,400 cells/mL3 without blast cells. CT scan of abdomen and pelvis with intravenous contrast showed ascites along with increased edema and wall thickening involving the ascending colon and proximal transverse colon (Figure 1). Colonoscopy revealed an ulcerated, friable mass with contact bleeding from the cecum to mid-transverse colon (Figure 2). Biopsies of the mass showed prominent diffuse proliferation composed of large immature cells with delicate chromatin and prominent nucleoli with frequent mitotic figures (Figures 3 and 4). Immunohistochemistry stains were positive for CD34 and myeloperoxidase and negative for PAX5 and CD3, findings compatible with myeloid sarcoma. Bone marrow biopsy showed a hypocellular marrow with no morphologic evidence of acute leukemia. However, ascites fluid cytology showed presence of blast cells. Given that her extramedullary relapse of AML conferred a very poor prognosis, the patient was transitioned to hospice care and passed away 1 month later.Myeloid sarcoma (MS) is an extramedullary tumor of immature granulocytic cells with an incidence of 2-9% in patients with AML. Although the GI tract is involved approximately 10% of cases, colorectal MS is extremely rare. Clinical presentations of MS in the GI tract are varied, ranging from asymptomatic to abdominal pain, small bowel obstruction, diarrhea, or hemorrhage. The diagnosis requires a high index of suspicion, as radiographic and endoscopic findings are non-specific. Confirmation of the diagnosis is based on histology and immunohistochemistry profiling, including positive staining for Myeloperoxidase (MPO), CD43, CD68, lysozyme, and CD117. Every patient diagnosed with MS should undergo a bone marrow biopsy. Treatment options depend on tumor site and size, patient's age, performance status, and previous treatment for AML (if any). First line treatment for MS is chemotherapy. Appropriate patients should undergo evaluation for bone marrow transplantation. Local therapy, including surgery and/or radiotherapy, could also be offered to selected patients depending on clinical symptoms.1646_A Figure 1. CT scan of abdomen and pelvis with IV contrast showed increased edema and wall thickening in the ascending and proximal transverse colon (arrow) and ascites.1646_B Figure 2. Colonoscopy revealed ulcerated friable mass with contact bleeding in cecum, ascending colon and transverse colon.1646_C Figure 3. Low magnification photomicrograph demonstrates sharp contrast between unremarkable (left) and abnormal (right) mucosal fragments, H&E stain, 40x. Note how the abnormal fragment has surface erosions (arrows). 4: High magnification image reveals cytomorphologic features of malignant mucosal infiltrate to include increased nuclear to cytoplasmic ratios, delicate chromatin and prominent nucleoli. Many atypical mitotic figures are present (arrows) and numerous apoptotic bodies are identified (arrowheads), H&E, 400x.