S3260 Think Outside the Marrow: A Rare Case of Acute Myeloid Leukemia Presenting With Pancreatic Head Mass

Introduction: Myeloid sarcoma, also known as granulocytic sarcoma or chloroma, is an extramedullary tumor made up of immature myeloid cells, typically in the context of acute myeloid leukemia (AML). Extramedullary AML can present a diagnostic dilemma for clinicians, especially in the setting of uncommon organ involvement. Here we discuss a rare case of myeloid sarcoma presenting with pancreatic head mass and obstructive jaundice. Case Description/Methods: A 72-year-old man presented with 4 months of vague epigastric abdominal pain and computed tomography abdomen/pelvis with findings of ill-defined, low-density mass concerning for pancreatic malignancy. Complete blood count and hepatic function panel at that time were within normal limits. He underwent endoscopic ultrasound which showed abrupt cut off of the main pancreatic duct at the pancreatic head and genu with subtle appearing 19 mm × 15 mm mass at the area. Fine needle biopsies were performed which resulted as chronic pancreatitis. Repeat imaging 1 month later reaffirmed presence of enlarging pancreatic mass and another endoscopic ultrasound was performed. This showed 19 mm × 25 mm irregular mass in the genu of the pancreas. Biopsies were again consistent with chronic pancreatitis. Three months later he presented to the emergency department with obstructive jaundice (bilirubin 5.4), elevated AST, ALT, and alkaline phosphatase and leukopenia with severe neutropenia (ANC 240). Peripheral smear showed many circulating blasts. Computed tomography showed further enlargement of previously seen pancreatic mass with new intra and extrahepatic biliary ductal dilatation. He underwent endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasound which showed malignant-appearing biliary stricture which was treated with sphincterotomy and covered metal stent placement. Endoscopic ultrasound identified a mass in the pancreatic head, T2 N1 by endosonographic criteria. Fine needle biopsy was performed of the mass and an adjacent lymph node. Both samples were consistent with AML. He underwent bone marrow biopsy which was also consistent with AML and chemotherapy was initiated. Discussion: Incidence of extramedullary disease (EMD) in AML may be as high as 25-30%, typically occurring in the lymph nodes, spleen, and liver. Although EMD is common, pancreatic involvement of AML is exceedingly rare with only a few case reports in the literature. Many of these cases describe diagnosis of AML after surgical intervention. Bone marrow involvement of AML, such as in this case, may be present. It is important for clinicians to consider myeloid sarcoma when presented with these scenarios, particularly in the setting of vague workup.