Calcifying Fibrous Pseudotumor of the Pancreas in a Patient With Metastatic Mammary Lobular Carcinoma and Gastric Gastrointestinal Stromal Tumor: A Previously Undescribed Benign Mimic of Metastatic Disease

Calcifying fibrous pseudotumor, a benign spindle cell tumor, has not been reported previously in the pancreas. Herein, we report a case of pancreatic calcifying fibrous pseudotumor in a 74-year-old female with a history of metastatic breast carcinoma and gastric gastrointestinal stromal tumor (GIST), both confounding the diagnosis and rendering it more challenging. Microscopic examination showed a well-demarcated, paucicellular, densely fibrotic tumor with widespread dystrophic calcifications and sparse, cytologically bland polygonal and spindle cells. Histologic and immunohistochemical work-up helped to exclude relevant differential diagnoses, including metastatic carcinoma, solitary fibrous tumor, inflammatory myofibroblastic tumor, and GIST.