Lessons to be learned: a case study approach. Malignant melanoma of soft tissue.

Malignant melanoma of soft tissue, also called clear cell sarcoma (CCS) of tendons and aponeuroses, presents as a soft tissue mass, usually in the lower extremity of young females. We report two cases of CCS of the upper extremity--in a Korean and a Saudi Arabian girl. Because of the presence of melanin, melanosomes, S-100 protein and the tendency for regional nodal metastases, it has been suggested that this entity be considered a melanoma rather than a soft tissue sarcoma. The evidence for a neuroectodermal origin of these neoplasms is compelling. Despite these features, CCS has been reported as showing a distinct chromosomal translocation pattern t(12;22)(q13;q12) in certain isolated cytogenetic or molecular diagnostic case reports; however, there is no information about the breakpoints at genomic level. Such genetic studies need to be performed on primary and metastatic cutaneous, mucosal or ocular melanomas prior to considering them specific for malignant melanoma of soft tissue/CCS. Microscopically, solid nests and fascicles of pale fusiform or cuboidal cells are divided by fine fibrous tissue septa. Characteristically, the cells possess a round to oval nucleus with a central prominent nucleolus. Pleomorphism may or may not be present; the cytoplasm is clear due to the presence of glycogen but, occasionally, the cytoplasm is more eosinophilic, resembling a melanoma. A tumour size (> or = 5 cm) and the presence of necrosis are statistically significant predictors of poor prognosis. A lesion on the proximal part of an extremity progresses slower than one that is more distal (i.e. acral). An early diagnosis and initial radical surgery are essential for a favourable clinical outcome. Once regional lymph node metastases or haematogenous dissemination has occurred, the prognosis becomes dismal.