Absence of mutations of the BRAF gene in malignant melanoma of soft parts (clear cell sarcoma of tendons and aponeuroses)

Malignant melanoma of soft parts (MMSP), also called clear cell sarcoma of tendons and aponeuroses, is cytogenetically characterized by the t(12;22)(q13;q12) resulting in the chimeric EWSR1/ATF1 gene. MMSP shares a number of morphologic, histologic, and immunohistochemical features with malignant melanoma of the skin, causing diagnostic difficulties in the distinction between MMSP and metastatic malignant melanoma with an unknown primary site. Recently, a high incidence of activating mutations in the kinase domain of the BRAF gene has been reported in malignant melanoma of the skin. The most common mutation (V599E) is the T1796A substitution in exon 15, leading to an exchange of valine for glutamic acid at position 599. Because of the extensive clinical, histologic, and immunohistochemic similarities with melanoma, we decided to analyze whether MMSP also has mutations in the BRAF gene. Eight MMSP with an EWSR1/ATF1 chimeric transcript, one soft tissue metastasis of a malignant melanoma of the skin, and one malignant melanoma cell line were examined. Both conventional melanomas had the exon 15 T1796A (V599E) mutation, but none of the MMSP was found to harbor any mutation in exon 11 or 15 of the BRAF gene. Our data further emphasize that MMSP and conventional malignant melanoma develop through different genetic pathways.