Dissecting the presence of malignant squamous cells in pancreatic cytopathology: A case series.

The presence of malignant squamous cells in pancreatic cytopathology is a rare phenomenon that results either from a primary or a metastatic process. Pancreatic adenosquamous carcinoma (PASC) represents the most common variant of pancreatic ductal adenocarcinoma and is associated with a dismal prognosis. Within the period of 2013-2018, the archives of "Hygeia and Mitera Hospital" were searched for pancreatic cytopathology-related diagnoses that included the interpretation of "malignant squamous cells present." All fine needle aspirations (FNAs) of pancreatic lesions, including liver metastases in patients with known pancreatic primaries, were retrieved along with their relevant clinical information. Five pancreatic and two liver FNAs acquired from a total of six patients were reexamined. None of these patients had any documented history of primary squamous malignancy elsewhere. All pancreatic and one of the two liver FNAs showed malignant squamous cells, identified based on either morphology or immunochemistry. The other liver FNA represented a metastatic deposit which comprised of only a glandular component, whereas the associated pancreatic FNA exhibited both squamous and glandular counterparts. Most cases characteristically showed necrosis and keratinization. Of interest, two cases revealed the presence of tumor-associated giant cells. In conclusion, the presence of malignant squamous cells in pancreatic FNAs could mean the presence of PASC, especially when there is no documented history of a primary malignancy and a complete clinical and imaging workup has been performed. Immunochemistry on cell block material could help to confirm squamous differentiation in the absence of overt keratinization.