Radiologic-pathologic discrepancy in the tumor size assessment of pancreatic ductal adenocarcinoma in the era of preoperative therapy.

Tumor size plays a central role in the staging, resectability assessment, and response evaluation of pancreatic ductal adenocarcinoma (PDAC). However, radiologic tumor size does not necessarily correspond to pathologic tumor size, and this discrepancy has become more clinically relevant in the preoperative therapy era. PDAC is characterized by infiltrative growth, abundant desmoplastic stroma, and ill-defined tumor borders, all of which complicate accurate size assessment on imaging. After preoperative therapy, fibrosis, necrosis, and scattered residual tumor cells further obscure the relationship between radiologic abnormalities and viable tumor burden. This review summarizes the mechanisms underlying radiologic-pathologic discrepancies in tumor size assessment of PDAC, with a focus on computed tomography, magnetic resonance imaging, ultrasound, and pathologic evaluation after preoperative therapy. We also discuss the prognostic implications of imaging-based and pathological tumor sizes and highlight the limitations of size-based response assessment. Finally, we review emerging approaches beyond conventional size metrics, including functional imaging, radiomics, and pathological standardization. Recognizing the biological and treatment-related basis of tumor size discrepancy is essential for improving tumor assessment and refining staging strategies in contemporary PDAC management.