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Introduction: Solitary fibrous tumor (SFT) is a fibroblastic tumor with malignant potential that is underpinned by a recurrent inv12(q13q13)-derived NAB2::STAT6 fusion. Breast and axilla are uncommon locations for this entity. Methods: Records of two academic institutions were electronically searched for breast and axillary SFTs. Clinical and pathologic data were reviewed. Literature review for breast or axillary SFTs was performed. Present study and previously reported tumors were stratified using five SFT risk models: original and modified Demicco metastatic risk, Salas local recurrence risk, Salas metastatic risk, and Thompson local recurrence risk. Results: Five patients with breast or axillary SFT were identified. Median age was 49 years, and median follow-up (available for four patients) was 82 months. Three patients showed no evidence of disease, and one developed recurrence. Literature review identified 58 patients with breast or axillary SFT. Median age was 54 years, and median follow-up (available for 35 patients) was 24 months. Thirty-one patients showed no evidence of disease, three developed recurrence, and one developed metastasis. Original and modified Demicco models and Thompson model showed the highest sensitivity; original and modified Demicco models and Salas metastatic risk model demonstrated the highest specificity. Kaplan–Meier models were used to assess recurrence-free probability (RFP). Original and modified Demicco models predicted RFP when stratified by "low risk" and "moderate/intermediate and high risk" tumor, though sample size was small. Conclusions: While many SFTs of breast and axilla remain indolent, a subset may develop recurrence and rarely metastasize. The modified Demicco risk model demonstrated optimal performance characteristics. [ABSTRACT FROM AUTHOR]

Establishing the etiology of a retroperitoneal tumor may be difficult due to close proximity of multiple organs. Evaluation of retroperitoneal tumors often leads to surgery, many times to obtain a definitive diagnosis and rule out malignancy. Calcifying fibrous tumors (CFT) are very rare soft tissue tumors occurring most often in young patients. They are most often found arising in the thoracic cavity, mediastinum, abdominal cavity and extremities and usually have a benign clinical course. Macrocscopically, the tumors are well circumscribed and firm with a white-tan appearance. Histologically, CFT comprised a hypocellular proliferation of bland spindle cells, densely hyalinized collagen, chronic lymphoplasmacytic inflammation and dystrophic calcifications. Other considerations in the pathologic differential diagnosis include solitary fibrous tumor and inflammatory myofibroblastic tumor. [ABSTRACT FROM AUTHOR]