Solitary Pancreatic Extramedullary Plasmacytoma Diagnosed Through Endoscopic Ultrasound-Guided Fine-Needle Biopsy-The Role of Endoscopic Diagnosis and Multidisciplinary Approach: A Case Report and Literature Review.

Background and Clinical Significance: Primary pancreatic extramedullary plasmacytomas (EMP) are extremely uncommon, representing less than 0.1% of all pancreatic masses and being far more uncommon than secondary involvement by an underlying multiple myeloma. Case presentation: A 69-year-old male was found with a solitary pancreatic mass. Endoscopic ultrasound (EUS)-guided fine-needle biopsy (FNB) revealed a monoclonal plasmacytic proliferation with molecularly confirmed KRAS (A146V) and BRAF (G469V) mutations. Multidisciplinary assessment ruled out a secondary localization, thus leading to the ultimate diagnosis of primary pancreatic EMP. Conclusions: Reaching a definitive diagnosis of primary pancreatic EMP requires a negative bone marrow biopsy and histological confirmation of the plasma cell nature of the pancreatic process. As for the latter, EUS-FNB may be a pivotal technique to avoid upfront surgical procedures.