Pathology of tumours of soft tissue

Benign tumours of soft tissue are relatively common, and include lipomas, schwannomas, haemangiomas, and fibrous histiocytomas. Intermediate tumours can be locally aggressive (e.g. fibromatosis) or, rarely, metastasize. Malignant tumours of soft tissue, or sarcomas, are uncommon, with an annual incidence of about 2.5 per 100,000 population in the UK. They arise in limbs and girdles, trunk, retroperitoneum, mediastinum and head and neck, and more often in deep, rather than superficial, locations.The usual presentation is as a slow-growing mass that can attain a large size particularly in deep soft tissue or retroperitoneum. Sarcomas comprise many histological categories that are classified by their differentiation (i.e. type of mesenchymal tissue they are attempting to form). This can be identified by light microscopy and with the aid of immunohistochemistry and cytogenetics. Several types of sarcoma have specific chromosomal translocations, resulting in new fusion genes, which can be useful for diagnosis. Prognostic factors include tumour size, depth from surface, and grade. Grading incorporates histological subtype, mitotic count and the amount of necrosis; the grade is a component of the staging system. Local control is achieved by surgery with clear margins, and adjuvant therapy; metastases are treated by surgical excision or systemic chemotherapy. In some cases, notably gastrointestinal stromal tumours, targeted therapy with specific agents (e.g. imatinib) has proved successful. Optimal management of these rare tumours requires close collaboration between pathologists and clinicians, and referral where necessary to specialist centres with experienced multidisciplinary teams, preferably before biopsy.