Secondary pancreatic tumors in endoscopic ultrasound-guided fine-needle biopsy: Clinicopathologic characteristics and morphological diagnostic challenges.

Pancreatic metastases are rare and often difficult to diagnose, especially in limited tissue samples. However, accurate diagnosis is crucial for guiding appropriate clinical management. This study evaluates the clinical, radiologic, and pathologic features of pancreatic metastases, with a focus on morphological patterns that mimic common primary pancreatic tumors in endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) specimens. Among 1054 pancreatic neoplasms diagnosed over a nine-year period, 62 cases (5.9 %) were identified as metastases. The interval from initial diagnosis to pancreatic involvement ranged from synchronous presentation to 24 years. Most metastatic lesions (74 %, n = 46/62) presented as solitary masses, and 58 % (n = 26/45) were initially misinterpreted as primary pancreatic tumors on imaging. Histologically, 73 % (n = 45/62) were epithelial neoplasms, most commonly of renal origin (11 cases, 17.8 %), followed by lung (9, 14.5 %), cutaneous (6, 9.7 %), and Müllerian-derived tumors (6, 9.7 %). Among non-epithelial neoplasms, hematopoietic malignancies were most common (9, 14.5 %), followed by mesenchymal tumors (5, 8.1 %) and melanoma (3, 4.8 %). Several metastatic tumor types-including renal cell carcinoma, lung adenocarcinoma, breast carcinoma, gastrointestinal adenocarcinoma, Merkel cell carcinoma, and adult granulosa cell tumor-closely mimicked the histology of primary pancreatic neoplasms such as pancreatic ductal adenocarcinoma, neuroendocrine neoplasm, and solid-pseudopapillary neoplasms. Accurate diagnosis requires correlation with clinical history and a comprehensive ancillary workup, including immunohistochemistry. In summary, pancreatic metastases present a significant diagnostic challenge due to their overlap with primary tumors across clinical, radiologic, and histologic dimensions. A multidisciplinary diagnostic approach is essential to ensure accurate classification and optimal patient care.