Non-keratinizing immature squamous metaplasia in the pancreas mimicking malignancy: a diagnostic pitfall in cytology

This report describes a challenging case in which atypical immature squamous metaplasia was misinterpreted as malignancy. A 69-year-old man presented with abdominal pain and loss of appetite. Imaging revealed mild pancreatic duct dilation, parenchymal enlargement, and increased fat attenuation in the transverse mesocolon. Endoscopic ultrasound revealed a hypoechoic lesion in the pancreatic body. The serum amylase level was markedly elevated (1,785 U/L), consistent with acute pancreatitis. Repeated pancreatic juice cytology examinations demonstrated atypical epithelial clusters, which raised concerns about possible pancreatic ductal adenocarcinoma. Therefore, distal pancreatectomy with splenectomy and transverse colon resection were performed. However, histopathological examination revealed only atypical immature squamous metaplasia. Retrospective review of the cytological specimens showed overlapping cell clusters with coarse chromatin, prominent nucleoli, nuclear pleomorphism, and peripheral dissociation in a neutrophilic background with focal hemorrhagic necrosis. Although rarely encountered, squamous metaplastic cells can appear in pancreatic cytology and represent a potential pitfall by mimicking adenocarcinoma.