So-called fibrohistiocytic tumours

Abstract

Fibrohistiocytic tumours are surrounded by controversy in their origin; its detailed description is beyond the scope of the current chapter. It is a popular term in the imaging literature, describing a lesion with histiocytic and fibroblastic appearances. It is categorised according to its malignant potential into (1) benign and (2) intermediate fibrohistiocytic lesions. Tenosynovial giant cell tumours have more in common with the descriptive category of fibrohistiocytic lesions than with true synovium. The current 2013 WHO soft tissue tumour classification has evolved since the 2002 edition, reflecting the cytogenetic and molecular genetic characterisation of these entities (Fletcher et al. WHO classification of tumours of soft tissue and bone, 2013). The most significant change seen to the classification of ‘so-called fibrohistiocytic tumours’ has been the removal of the malignant counterpart of benign fibrohistiocytic tumours, ‘malignant fibrous histiocytoma’ (MFH) and its subtypes. MFH is now synonymous with undifferentiated pleomorphic sarcoma and appears in a new category of ‘undifferentiated/unclassified sarcomas’ (see Chap. 19). Furthermore, fibrohistiocytic lesions that have a predilection for the skin are described separately in the WHO classification of skin tumours. Dermatofibrosarcoma protuberans and giant cell fibroblastoma are described under the ‘fibroblastic/myofibroblastic tumours’ category. Angiomatoid fibrous histiocytoma and atypical fibroxanthoma are now described under the ‘tumours of uncertain differentiation’ category.