Acquired BRAF Gene Mutations in Pleural Malignant Mesothelioma: A Potential Therapeutic Target.
Charlene F Hellman, Mohammad A Vasef, James M Gale, Khalil Sheibani. University of New Mexico, Albuquerque; TriCore Reference Laboratories, Albuquerque, NM; Western Medical Center, Santa Ana, CA
Background: Pleural malignant mesothelioma (PMM) remains an aggressive tumor with a short median survival and a poor response to conventional treatment modalities. Current treatments, including chemotherapy, radiotherapy, and surgical resection, are aimed mainly at palliation. Research into alternative therapies using molecular targeted therapy, gene therapy, and immunotherapy has not been conclusive at this time. Profiling of the genetic alterations responsible for tumorigenesis is needed to advance our understanding of the disease and guide future research efforts. Somatic missense mutations in the BRAF gene have been identified in a variety of human cancers but have not been reported in PMM.
Design: From the consultation files of one of the authors (KS), paraffin blocks from 40 cases of immunohistochemically confirmed PMM including various histologic subtypes with adequate tumor were pulled to assess for mutations in the BRAF gene. Briefly, DNA was extracted from paraffin blocks using QIAamp DNA FFPE Tissue Kit (Qiagen). A 107 base pair in length region of the BRAF gene, including codon 600, was amplified by Real-Time PCR on the LightCycler (Roche) and subjected to high resolution melting curve analysis using the HR-1 High Resolution Melting Instrument (Idaho Technologies). Known BRAF wild type and BRAF V600E mutant DNA samples were included as negative and positive controls respectively. All samples with an abnormal melting curve that was not aligned with the wild type melting curve, and was suggestive of a mutation, were further examined by direct DNA sequencing in both forward and reverse directions using BigDye Terminator Cycle Sequencing kit (Applied Biosystems) on an ABI PRISM 3100 Genetic Analyser.
Results: Of 40 PMM, 2 (5%) harbored a BRAF mutation. One sarcomatoid subtype demonstrated BRAF V600E, the most common BRAF mutation seen in malignant melanoma, papillary thyroid carcinoma, colorectal cancers, and other human malignancies. The second case with mixed epithelial and sarcomatoid histologic subtype revealed a novel BRAF D587G mutation.
Conclusions: BRAF is mutated in PMM at a low frequency. Given the dismal prognosis of PMM, the small subset of patients who demonstrate activating BRAF mutations in their tumors may benefit from the administration of new BRAF kinase inhibitors (such as PLX4032) that have shown promising results in clinical trials enrolling patients with BRAF V600E mutated melanoma.
Tuesday, March 1, 2011 1:00 PM
Platform Session: Section F, Tuesday Afternoon