Clear cell sarcoma C43.-

Enzinger 1965

Rare malignant tumor of neuroectodermal origin. It is also called malignant melanoma of the soft tissues due to its ability to synthesize melanin.

Characteristic chromosome translocation t(12;22)(q13;q12); several gene fusion transcripts are observed: most frequent (about 87%) EWSR1 exon 8 fusion to ATF1 exon 4 (type 1), EWSR1-ATF1 type 2-4 about 10% of cases, very rare also translocation t(2;22)(q32;q12) with CREB1-EWS gene fusion (mostly gastrointestinal tumors).

Fascicular or nest-like pattern with spindle-shaped, polygonal, eosinophilic cells. The cytoplasm is light to basophilic, the nucleus ovoid and vesicular with a prominent, mostly eosinophilic nucleolus. The proportion of fibrous stroma is variable. Mitoses are rare in most clear cell sarcomas. Necroses or multinuclear giant cells are found in about half of the tumors. A junctional activity, as is to be expected in malignant melanoma, is usually completely absent or only hinted at. Immunohistology: HMB-45, melan-A and/or S-100 protein positive in most clear cell sarcomas. In contrast to melanoma, however, BRAF, NRAS and KIT mutations are usually not found. Intracellular melanin may be detectable, cytokeratin is not detectable. Typically, t(12;22)(q13;q12) translocation with an EWSR1 (Ewing sarcoma breakpoint region 1 gene)-ATF1 fusion can be detected in >90% of tumors, more rarely an EWSR1-CREB1 fusion (CREB1=acronym for cAMP responsive element binding protein1).

Clinically, the diagnosis cannot be guaranteed. A histological clarification including immunohistochemistry must be performed. The diagnosis is ultimately confirmed by FISH analysis or RT-PCR by detecting the above characteristic chromosome translocation. The TNM classification, stage classification and grading is carried out according to UICC/AJCC 2002 or French Federation of Anticancer Centers (FNCLCC)

1. Falconieri G et al (2012) Cutaneous Clear Cell Sarcoma: Report of Three Cases of a Potentially Underestimated Mimicker of Spindle Cell Melanoma. Am J Dermatopathol Epub ahead of print
2. Gambichler T et al (2012) Deep intronic point mutations of the KIT gene in a female patient with cutaneous clear cell sarcoma and her family. Cancer Genet. 205:182-5
3. Hantschke M et al (2010) Cutaneous clear cell sarcoma: a clinicopathologic, immunohistochemical, and molecular analysis of 12 cases emphasizing its distinction from dermal melanoma. On J Surg path. 34:216-22.
4. Langezaal SM et al (2001) Malignant melanoma is genetically distinct from clear cell sarcoma of tendons and aponeurosis (malignant melanoma of soft parts). Br J Cancer. 84:535-8
5. Meis-Kindblom JM. (2006) Clear cell sarcoma of tendons and aponeuroses: a historical perspective and tribute to the man behind the entity. Adv Anat Catholic. 13:286-92
6. Song JS et al (2010) Diagnostic utility of EWS break-apart fluorescence in situ hybridization in distinguishing between non -cutaneous melanoma and clear cell sarcoma. Catholic Int. 60:608-13.