BRAF and NRAS mutational status in clear cell sarcoma

Abstract

9000 Background: Clear-cell-sarcoma (CCS) also known as melanoma of the soft parts (MSP) is a rare cancer of adolescents and young adults arising in the deep soft tissues. Several clinical and pathological data demonstrate features typical of melanoma (the propensity for lymph node metastasis, expression of melanoma markers:HMB45, S100. Conversely, deep location in the soft tissues and recurrent t(12;22) translocation coding for the fusion protein EWS-ATF1 are rather suggestive of soft tissue sarcoma (STM). Data comparing gene expression profiles of CCS, melanomas and STM showed that CCS clustered with melanoma rather than with STM. BRAF mutations are frequently found in cutaneous melanoma (40–60%) but are not found in distinct melanoma subtypes(mucosal or uveal). Upstream of BRAF, on the same MAP kinase pathway NRAS is also frequently mutated in melanoma, with a mutually exclusive spectrum of mutations for these two genes. Our objective was to evaluate the frequency of BRAF and NRAS mutations is CCS. Methods: DNA was prepared from paraffin-embeded tissues of 22 CCS carrying the t(12;22) translocation and six melanoma. PCR amplification of BRAF exons 11 and 15 as well as NRAS codons 12, 13 and 61 were performed and PCR products were sequenced. Phosphorylation of ERK was studied using an anti-phospho-ERK antibody SIGMA). Results: Only one of the 22 CCS harboured a BRAF mutation (V599E) (4.5%). Two mutations of NRAS (codon 61) were also found with no overlap with the BRAF mutation. Among the 6 melanomas, one had a BRAF (V599E) and three others had a NRAS mutation. Immunostaining with the anti phospho-ERK antibody showed faint positivity in 8/14 CCS. Among the 6 melanoma, 4 displayed ERK phosphorylation, which was strictly correlated to the presence of NRAS or BRAF activating mutations. Conclusions: BRAF and NRAS mutations are rarely present in CCS. Only 1/22 BRAF mutation and 2/22 NRAS mutation were found. in our serie. These results suggest that although genomic profiling showed that CCS clustered with melanoma, most of them occur independently of BRAF and NRAS mutations frequently found in cutaneous melanoma. No significant financial relationships to disclose.