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Understanding

Classification

Definition

Soft tissue sarcomas (STS) are tumours derived from non-epithelial extraskeletal tissues including muscle, fat and fibrous supporting structures, arising mainly from the embryonic mesoderm, with some neuroectodermal contribution1. They can occur anywhere in the body but most commonly arise in the limbs (approximately 50% of cases). Other common sites include the gastrointestinal (GI) tract (25%of cases), retroperitoneum (15–20% of cases) and head and neck (approximately 9% of cases)2.

Histopathology

STS are a heterogeneous group of diseases, with distinct histological, cytological and molecular features. Tumours are classified histologically according to the soft tissue cell that they resemble. At macroscopic examination, STS generally present as tan-white masses with a fish-flesh appearance.

The major histological types of STS may be divided into several subtypes depending on genetic abnormalities and large differences in disease history. Prognosis is based on the histoprognostic grade of the tumour. Of the several grading systems available, the most widely accepted is the classification proposed by the French Federation of Cancer Centers Sarcoma Group3. This classification has demonstrated prognostic value for predicting the risk of local relapse, metastatic spread or death, with 5-year survival rates of 95%, 75% and 45% in patients with grade 1, 2 or 3 tumours, respectively4. The histological classification of STS is under continuous revision and subtypes.

For example, gastrointestinal leiomyosarcomas which have been shown to express the tyrosine kinase receptor c-kit, have been requalified as Cajal cell tumours or gastrointestinal stromal tumours (GIST). Other histopathological or molecular entities will likely be identified through the ongoing development of new molecular biology techniques5.

Major histological types of adult soft tissue sarcomas
Histological type%
Fibrosarcomas or MFH 43%
Liposarcomas 13%
Synovialosarcomas 9%
Leiomyosarcomas 8%
Rhabdomyosarcomas 5%
Neurosarcomas 4%
Unclassified tumors 5%
Others (unclassified) 9%
From Coindre, et al. J Clin Oncol. 1996;14:869

References:
1. Clark MA, Fisher C et al. (2005) “Soft-tissue sarcomas in adults.” N Engl JMed 353(7): 701–11.
2. NCCN Clinical Practice Guidelines in Oncology™. Soft Tissue Sarcoma V3, 2007. http://www.nccn.org. Accessed Novemeber 2007.
3. Erba E, Bergamaschi D, Bassano L, et al. Ecteinascidin-743 (ET-743), a natural marine compound, with a unique mechanism of action. Eur J Cancer. 2001;37:97-105.
4. Le Cesne A, Blay JY, Judson I, et al. Phase II study of ET-743 in advanced soft tissue sarcomas: a European Organisation for the Research and Treatment of Cancer (EORTC) soft tissue and bone sarcoma group trial. J Clin Oncol. 2005;23(3):576-84. Erratum in: J Clin Oncol. 2005;23(22):5276.
5. Van Glabbeke M, Verweij J, Judson I, Nielsen OS. Progression-free rate as the principal endpoint for phase II trials in soft-tissue sarcomas. Eur J Cancer. 2002;38:543-9.