Primary pancreatic Ewing sarcoma: a cytomorphologic and histopathologic study of 13 cases.

Introduction: Ewing sarcoma (ES) is a small, round cell sarcoma that rarely occurs in solid organs, including the pancreas. A diagnostic overlap exists with other primary pancreatic neoplasms, especially for specimens from small biopsies and fine needle aspiration (FNA). To improve the diagnosis of this rare pancreatic tumor, we have reported a series of 13 cases of primary pancreatic ES and reviewed the cytopathologic, surgical pathology, clinical, and radiologic features of these neoplasms.

Materials And Methods: We performed a retrospective case review of 13 patients with a diagnosis of pancreatic ES from 2 tertiary academic medical centers. A combination of cytology and histopathologic slides were reviewed, and the patient demographics, clinical information, somatic genetics, and radiologic findings were obtained from the electronic medical records.

Results: Five FNA specimens from 5 patients and 8 surgical biopsy or resection specimens were identified and reviewed. The patients included 9 males and 4 females, with a median age of 27 years (range, 15-78 years). The cytology smears were highly cellular and showed a combination of complex tissue fragments and singly dispersed small round blue cells. The final diagnosis was ES for all 5 FNA specimens in accordance with the characteristic cytomorphology, diffuse and/or strong membranous immunolabeling for CD99, membranous β-catenin, and molecular confirmation of EWSR1 using fluorescence in situ hybridization or reverse transcriptase polymerase chain reaction.

Conclusions: The cytologic diagnosis of ES is challenging, especially in unusual locations such as the pancreas. However, the correct cytologic diagnosis is important because these patients will require neoadjuvant therapy before surgery. Confirmatory molecular studies should be required to render the diagnosis of pancreatic ES.