Classification of soft tissue sarcomas
Soft tissue sarcomas (STSs) represent less than 1% of all malignant tumours and benign mesenchymal tumours are at least 100 times more frequent than sarcomas.
The World Health Organization (WHO) classification recognises >50 histological sarcoma types. The diagnosis should be made by a multidisciplinary team and the histological diagnosis should be confirmed by an expert pathologist.
Histological classification of soft tissue tumours is based on the line of differentiation (resemblance to normal tissue counterpart) of the tumour.
Each histological subgroup is divided into:
- benign: low rate of non-destructive local recurrence, no metastasis
- intermediate, locally aggressive: no metastatic potential, but high rate of local recurrence, with destructive growth pattern, requiring wide excision, e.g. desmoid-type fibromatosis
- intermediate, rarely metastasising: locally aggressive, and well-documented metastatic potential (<2% distant metastases)
- malignant (sarcoma): locally destructive and significant risk of distant metastases (most often 20%–100%).
Note that the intermediate category does NOT correspond to the Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) histological intermediate grade (Grade 2) of malignancy.
The aetiology of most benign and soft tissue tumours is unknown.
Soft tissue tumours can occur on a familial or inherited basis. Examples of hereditary syndromes with soft tissue tumours include: desmoid-type fibromatosis in patients with familial adenomatous polyposis, peripheral nerve sheath tumours and gastrointestinal stromal tumours (GISTs) in patients with neurofibromatosis, and sarcomas in Li-Fraumeni syndrome.
Rarely, sarcomas are associated with previous radiation, viral infection or immunodeficiency.
REVISION QUESTIONS
1. To which histological subgroup do liposarcomas belong?
2. What is known about the aetiology of STSs?
3. What does it mean when a tumour is classified in the intermediate category?
Preface WHO classification of soft tissue sarcomas: use of immunohistochemistry
