Malignant melanoma of the soft parts is an old name for Clear cell sarcoma of the soft tissue

this tumour, initially described by Enzinger as clear cell sarcoma of tendons and aponeuroses, is of uncertain origin, but its immunohistochemical profile shows its melanocytic nature; however it has no genetic relationship with the cutaneous malignant melanoma

being of melanocytic origin, this tumour should be classified as a neuroectodermal tumour

unknown

it is a very rare tumour representing a minority of all soft tissue sarcomas

the malignant melanoma of soft parts (MMSP) preferentially occurs in young adults, between ages of 20 and 40 years; the tumour develops mainly in the extremities, especially the legs (foot, knee, heel, ankle); it is usually deeply seated, and often bound to tendons and aponeuroses

the tumours show compact nests and strands of round or fusiform cells with a clear cytoplasm, separated by fibrocollagenous tissue often connected to adjacent tendons or aponeuroses; mitotic index is generally low; the cells of nearly all cases express S-100 protein and the melanoma-associated antigen HMB45

the treatment protocols vary greatly according to the intitutions; however, the melanoma of soft parts is a highly malignant tumour which requires surgical excision combined with radiotherapy and/or chemotherapy

many patients develop recurrences and regional and distant metastases, in lymph nodes, lung, and bones; in the series of Enzinger, the average time between diagnosis and recurrence was 2.6 years, between diagnosis and metastasis, 3.5 years

the prognosis is poor; in the series of 115 patients studied by Enzinger, 46% had died; of the 62 living patients, 21 experienced one or more recurrences, and 7 had a metastatic disease

this tumour is characterised by the presence of a chromosome translocation t(12;22)(q13;q12), which involves genes ATF-1, on chromosome 12, and EWS, on chromosome 22

EWSR1 (Ewing sarcoma breakpoint region 1)

22q12.2

RNA binding protein

ATF1 (activating transcription factor 1)

12q13.12

transcription factor

the chimaeric protein is composed of the N-terminal domain of EWS linked to the bZIP domain of ATF-1

binds to ATF sites present in cAMP-responsive promoters via the ATF1 bZIP domain and activates transcription constitutively, dependent on the activation domain (EAD) present in EWSR1