[The histological features of local recurrences of soft tissue sarcomas].

Local recurrence is a well-recognised problem in soft tissue sarcomas, especially at difficult anatomical locations or after inadequate surgery. It is logical to assume that such recurrence will have an adverse effect on prognosis. In most cases the histological appearance of the recurrence is very similar to that of the primary neoplasm, in view of the fact that recurrence is most common in high-grade (poorly differentiated) sarcomas. However, in some cases, the appearance may change in one of three ways: (1) Gradual progression in grade. This phenomenon is seen most often in leiomyosarcoma or myxofibrosarcoma, in which the tumour shows progressive loss of differentiation and there is increasing risk of metastasis; (2) Abrupt change to a higher grade. This phenomenon, known as dedifferentiation, is commonest (among soft tissue lesions) in liposarcoma and is characterised usually by the emergence of an "MFH-like" pattern and an increased risk of metastasis; (3) Acquisition of differentiation. Some round cell sarcomas in children become better differentiated after chemotherapy, and some dedifferentiated adult sarcomas may revert to their well-differentiated form; occasionally the appearance of greater differentiation reflects sampling error in the primary tumour. Pathologists should be aware that significant morphological changes may occur in recurrent soft tissue sarcomas and, in analysing and diagnosing such lesions, they should always review material from the primary tumour.