Clear cell sarcoma (malignant melanoma of soft parts)

Epidemiology

  The tumour is found across a wide age from the second decade onwards, with a mean or 30 years and 70% of cases occurring before the age of 40 years. The sex predominance has varied across studies.

Clinical features

Most tumours arise in the deep soft tissues of the extremities, with lesser numbers in the trunk and limb girdles.

Macroscopic appearances

The tumour most commonly arises in aponeuroses and tendons or in skeletal muscle.

Histopathology

The tumour cells are fairly uniform, spindled, forming nests or short fascicles. Some cases also show sheets of epithelioid cells. Loss of cellular cohesion may result in an alveolar pattern. Other cases show a microcystic pattern. The tumour cells have clear, pale or eosinophilic cytoplasm. Nuclei have prominent nucleoli. A minority of cases include rhabdoid cells. There may be intracytoplasmic melanin. A few cases have a lymphocyte-rich stroma.

Immunohistochemistry

Cytogenetics

 There is a characteristic t(12;22)(q13;q12) translocation, resulting in a ATF1-EWSR1 fusion product. Clear cell sarcoma of the gastrointestinal tract may show an alterative translocation, characteristic t(2;22)(q3;4q12) translocation, which creates a CREB1-EWSR1 fusion product.

Prognosis

This is an aggressive tumour with a high mortality due to disseminated metastases. Tumour size and necrosis have been associated with aggressive behaviour.

References

1 Miettinen M et al. Microphthalmia transcription factor in the immunohistochemical diagnosis of metastatic melanoma: comparison with four other melanoma markers. Am J Surg Pathol 2001;25:205-211.

2 Hisaoka M, Ishida T, Kuo TT, et al. Clear cell sarcoma of soft tissue: a clinicopathologic, immunohistochemical, and molecular analysis of 33 cases. Am J Surg Pathol 2008; 32:452-60

This page last revised 27.4.2008

©SMUHT/PW Bishop