Pancreatic Solitary Fibrous Tumor: A Common Tumor Occurring in a Rare Location.

BACKGROUND The purpose of this report is to explore the clinicopathological characteristics, diagnosis, and differential diagnosis of primary solitary fibrous tumor (SFT) of the pancreas. This report provides a retrospective analysis of the clinical features, histopathological findings, and immunohistochemical profiles of 2 patients with pancreatic SFT, supplemented by a review of the relevant literature. CASE REPORT Both patients were postmenopausal women who were incidentally found to have pancreatic masses during routine physical examinations. Similarly, both patients were misdiagnosed with neuroendocrine tumors of the pancreas on imaging (CT or MRI). Neither patient exhibited symptoms in their daily lives. Microscopically, both cases revealed distinct spindle cell tumors with poorly defined margins within pancreatic tissue. The tumors exhibited an expansile growth pattern with cells arranged in bundle-like structures or in a disordered arrangement, showing no cellular atypia or mitotic activity. Antler-like vessels were observed in the tumor stroma, with no evidence of necrosis. However, one of the tumors showed a sparse density of tumor cells with prominent collagen fiber hyperplasia. Immunohistochemical analysis showed that both tumors exhibited nuclear expression of STAT6. CONCLUSIONS Pancreatic SFT is clinically rare, with an overall favorable prognosis. However, owing to the general lack of symptoms in patients and nonspecific imaging manifestations, it is often misdiagnosed clinically. Histologically, given its morphological diversity, it needs to be differentiated from spindle cell tumors such as pancreatic gastrointestinal stromal tumors, fibromatosis, inflammatory myofibroblastic tumors, and pancreatic sclerosing epithelioid fibrosarcoma. Nuclear expression of STAT6 and the presence of NAB2: : STAT6 fusion are important characteristics of SFT.