Myeloid sarcoma as a pancreatic cancer mimic: Refining the clinical differential of pancreatic masses

Abstract Introduction Myeloid sarcoma (MS) is a rare extramedullary tumor composed of immature granulocytes or monocytes and is an uncommon presentation of leukemia. Due to a low incidence, there is potential for error in omitting this condition in standard diagnostic heuristics. Here we describe the presentation of myeloid sarcoma as a pancreatic mass which became a harbinger of acute myeloid leukemia. Case A 40-year-old male presented to his primary care doctor with isolated painless jaundice of sudden onset without unintentional weight loss, fevers or chills. Initial labs revealed elevated liver enzymes with aspartate transaminase (AST) 93 U/L, alanine transaminase (ALT) 246 U/L, alkaline phosphatase 243 U/L, total bilirubin 11.2 mg/dL, direct bilirubin 7.66 mg/dL. His abdominal ultrasound revealed biliary sludge and mild dilatation of both intrahepatic and extrahepatic biliary ducts. The patient was then admitted for expedited workup. His CBC demonstrated WBC 6,210/mm3, Hg 12.9 g/dL, and Plt 417,000/mm3. A CT abdomen and pelvis with IV contrast demonstrated a 3.5 x 3.4 cm pancreatic head mass with moderate intrahepatic biliary dilation and a common bile duct measuring 1.6 cm. He underwent an endoscopic ultrasound (EUS) with endoscopic retrograde cholangiopancreatography demonstrating an irregular hypoechoic, heterogeneous, mixed solid and cystic mass in the pancreatic head measuring 4.0 x 3.6 cm. A fine needle aspiration (FNA) was performed using three passes of a 22-gauge biopsy needle, and an uncovered metal stent was deployed in the common bile duct to maintain patency. Cytology from the pancreatic head mass and a nearby lymph node were non-diagnostic and bile duct washings were negative, yet the suspicion for malignancy remained high. The patient subsequently underwent 2 additional EUS with FNA biopsy, yet both were non-diagnostic and yielded findings of chronic pancreatitis. However, there were only occasional plasma cells highlighted by CD38 and CD138 stains, insufficient for IgG4 staining. Serum IgG4 was marginally elevated at 170 mg/dL. He was started on steroids for possible autoimmune pancreatitis. Two months later, the patient presented to the hospital with abnormal labs. His CBC was notable for WBC count of 77,000/mm3, Hg 10.2 g/dL, Plt 41,000/mm3 with 62% myeloid blasts observed concerning for acute leukemia. A CT abdomen and pelvis demonstrated an interval increase in the size of his pancreatic head mass at 8.4 x 6.0 cm versus 4.2 x 4.1 cm previously. He received a final EUS and FNA of the pancreatic head demonstrating myeloid sarcoma, positive by immunohistochemistry (IHC) staining for CD45, CD34, CD117, MPO, and CD43 while being negative for CD20, CD79a and CD3. Flow cytometry noted that the CD34 blast population was moderately positive for CD33. The patient received a bone marrow biopsy that confirmed a hypercellular marrow involved by acute myeloid leukemia. Chromosomal analysis of the bone marrow biopsy demonstrated inv(16)/(p13.1q22) in all metaphases analyzed. Fluorescence in-situ hybridization demonstrated MYH11/CBFB fusions in 75.5% of nuclei and next-generation sequencing demonstrated gene fusions in CBFB-MYH11. These results were consistent with core-binding factor acute myeloid leukemia. The patient was initiated on hydroxyurea for initial leukoreduction. After receiving his bone marrow biopsy results with molecular characterization, he received induction therapy with gemtuzumab ozogamicin (3 mg/m2) and a 7-day infusion of cytarabine (100 mg/m2/day) with 3 days of concurrent daunorubicin (60 mg/m2). His WBC count improved markedly, and the peripheral blood blast count became undetectable. A CT abdomen and pelvis with IV contrast performed at the end of induction demonstrated that his pancreatic mass had regressed to 5.0 x 4.1 cm from a prior measurement of 8.4 x 6.0 cm. His bone marrow biopsy on count recovery demonstrated no morphologic evidence of acute myeloid leukemia. Discussion Myeloid sarcoma occurs in 2-8% of AML cases, and may arise simultaneously with AML, present as a relapse of AML, or occur de novo. In cases where MS occurs without evidence of another hematological malignancy, referred to as isolated MS, there may be difficulty achieving an accurate diagnosis since it may mimic other tumors. Adding IHC staining for CD43 and MPO can help reveal this diagnosis. Increased awareness and earlier diagnosis with intervention are critical to improved prognosis and reduced morbidity.