Anaplastic Carcinoma Arising in a Mucinous Cystic Neoplasm Masquerading as Pancreatic Pseudocyst

Mucinous cystic neoplasms (MCN) of the pancreas can vary from benign to premalignant and malignant. Preoperative diagnosis is essential to offer the patient appropriate treatment. Occasionally these cases may harbor anaplastic carcinoma while clinically masquerade as a pseudocyst. Here in, we report an unusual case of a 37-year old female presented with recurrent abdominal pain that was suspected clinically and by imaging studies to have a pseudocyst. EUS-FNA with internal drainage of the cyst was performed. Cytological evaluation of the cyst fluid showed numerous inflammatory cells composed mainly of many neutrophils admixed with macrophages reminiscent of the usual pseudocyst content but there were scattered rare dyscohesive malignant cells which were highly pleomorphic with multinucleation. Immunostains on the cell block showed immunoreactivity of these cells including the multinucleated cells for Cam 5.2 and AE1/AE3 and focally for Ber-Ep4, Moc -31, and CA19-9. The subsequent resection confirmed the presence of anaplastic (undifferentiated) carcinoma (AC) arising in a MCN of the pancreas. Diagn. Cytopathol. 2016;44:538-542. © 2016 Wiley Periodicals, Inc.