Rare pancreatic ductal adenocarcinoma variants and other malignant epithelial tumors: a comprehensive clinical and radiologic review.

Over 95% of pancreatic carcinomas are classified as conventional pancreatic ductal adenocarcinoma (cPDAC), while less than 5% consist of rare histological subtypes. Some of these rare histological subtypes, such as colloid carcinoma, medullary carcinoma, and undifferentiated carcinoma with osteoclast-like giant cells, are associated with a relatively better prognosis compared to cPDAC, whereas others, including signet ring cell carcinoma/poorly cohesive carcinoma, adenosquamous carcinoma, large cell carcinoma with rhabdoid phenotype, and undifferentiated carcinoma, have a worse prognosis. Other malignant pancreatic epithelial tumors (MPET) include acinar cell carcinoma, pancreatoblastoma, and solid-pseudopapillary neoplasm that should also be differentiate from PDACs. Accurate differentiation among PDAC subtypes and other MPETs is essential for precise survival predictions and effective therapeutic planning. However, cPDAC, rare histological subtypes of PDAC and MPETs often exhibit similar imaging findings, making it challenging to establish a diagnosis based solely on imaging. Thus, needle biopsy or surgical resection is generally required for the final diagnosis. We herein present a review article based on case studies and literature reviews of rare histological subtypes of PDAC and other MPET, with particular focus on their imaging characteristics, referencing the 5th edition of the World Health Organization classification.