Recurrent BRAF kinase fusions in melanocytic tumors offer an opportunity for targeted therapy

Area of Science:

• Oncology
• Genetics
• Molecular Biology

Background:

• BRAF is a prevalent oncogene and a key therapeutic target in melanoma.
• BRAF activation can occur through rearrangements fusing its kinase domain to partner genes.

Purpose of the Study:

• To investigate BRAF rearrangements as a mechanism of oncogene activation in melanoma.
• To characterize the therapeutic response of BRAF fusion-driven melanoma to targeted inhibitors.

Main Methods:

• Comparative genomic hybridization (CGH) analysis of 848 melanocytic tumors.
• DNA sequencing to identify and characterize BRAF fusions.
• In vitro studies using melanoma cell lines to assess pathway activation and drug sensitivity.
• Clinical response assessment in a patient with a BRAF fusion.

Main Results:

• BRAF kinase domain fusions with six different N-terminal partners were identified in 10 tumors.
• A novel BRAF fusion was found to constitutively activate the MAP kinase pathway in a melanoma cell line.
• Sorafenib inhibited MAP kinase pathway activation and proliferation in the BRAF fusion cell line at clinical concentrations.
• BRAF V600E mutant cell lines were more sensitive to vemurafenib, while the fusion cell line showed limited response.
• The patient with the BRAF fusion exhibited a durable clinical response to sorafenib.

Conclusions:

• BRAF fusions represent an alternative oncogenic mechanism in melanoma.
• Targeted therapy with sorafenib is effective against BRAF fusion-driven melanoma.
• Differential drug sensitivity exists between BRAF fusions and BRAF V600E mutations, necessitating distinct therapeutic strategies.