Extra-meningeal solitary fibrous tumor: an evolving entity with chameleonic morphological diversity, a hallmark molecular alteration and unresolved issues in risk stratification assessment.

Solitary fibrous tumor (SFT) is a rare type of mesenchymal lesion with variable clinical presentation in which specific clinicopathologic factors have been related to patient outcome. SFT shares an important morphologic and immunohistochemical overlap with other sarcomas, hence the differential diagnosis is challenging. Although molecular studies provide significant clues, especially in the differential diagnosis with other neoplasms, a thorough hematoxylin and eosin analysis and the integration of phenotypical, clinical, and radiological features remain an essential tool in SFT diagnosis. In this review, we discuss some emerging issues still under debate in SFT.

[Bone and soft tissue Langerhans cell histiocytosis with multinucleated giant cells and BRAF V600E mutation]. / Histiocitosis de células de Langerhans de partes blandas y hueso con células gigantes multinucleadas y mutación BRAF V600E.

Langerhans cell histiocytosis (LCH) is a heterogeneous disease characterized by proliferation of Langerhans cells and BRAF mutation in almost half of the cases. Bone involvement is common but large soft tissue disease is uncommon. We report a pediatric patient with a large tumor mass involving the left iliac bone and the adjacent soft tissue. The computed tomography scan showed an osteolytic lesion with soft tissue extension. Surgical curettage of the lesion was performed and the final histopathologic diagnosis was LCH with CD1a immunoreactivity in tumor cells. The molecular analysis revealed a BRAF V600E mutation. We discuss the histopathological and immunohistochemical differential diagnosis with histiocytosis other than LCH.