Fine-needle aspiration findings of a rare hematopoietic neoplasm presenting as obstructive jaundice

A 51-year-old female who presented with obstructive jaundice was found to have masses in the pancreatic head and tail as well as suspicious liver and periaortic masses on imaging. Aspiration cytology of the pancreatic tail mass showed abundant large single cells with vacuolated eosinophilic cytoplasm, marked nuclear pleomorphism, large bizarre irregular nuclei, binucleation, and prominent nucleoli. Numerous cells also showed intracytoplasmic black to brown pigmentation. A cell block was obtained and extensive immunohistochemical staining was performed. S-100, HMB-45, Sox10, pancytokeratin, CK7, RCC antigen, synaptophysin, HepPar 1, inhibin, CD45, CD21, and CD123 were negative, making melanoma, epithelial malignancies, lymphoma, follicular dendritic and plasmacytoid dendritic cell neoplasms less likely. CD4 and CD56 showed partial positivity, and CD68, CD163, and CD14 were positive, supporting the diagnosis of histiocytic sarcoma. Surgical specimens and immunohistochemistry confirmed the cytologic findings. Histiocytic sarcoma is a rare aggressive malignancy of histiocytic origin with most cases presenting in adults in extranodal sites, most commonly the intestinal tract. Few cases are reported in the literature, presenting diagnostic challenges for cytopathologists when seen on fine-needle aspiration. We present the first reported case of histiocytic sarcoma presenting as a pancreatic mass, diagnosed by endoscopic ultrasound guided fine-needle aspiration (EUS-FNA). This entity is rarely described on cytology and arose in a location in which EUS-FNA is the diagnostic modality of choice. This case study highlights that cytopathologists should be aware of histiocytic sarcoma occurring in extranodal locations accessible by EUS-FNA and be familiar with the cytomorphologic appearance.