[1729] Ras-MAPK Pathway Mutation Analysis in Cerebellopontine Angle Tumors

Matthew D Cykowski, Richard A Allen, Kar-Ming Fung, Ethan D Stolzenberg, S Terence Dunn. University of Oklahoma Health Sciences Center, Oklahoma City, OK

Background: Activity in the RAS-mitogen associated protein kinase (MAPK) signaling pathway can be altered in neurofibromatoses type 1 (NF1) and 2 (NF2) where the loss of tumor suppressors can lead to elevated MAPK activity and tumorigenesis (e.g., bilateral vestibular schwannomas (VS) and meningioma in NF2). Alternatively, activating mutations in B-raf and/ or Ras components of the Ras-MAPK pathway can lead to increased mitogenic signaling. One recent investigation of nerve sheath tumors identified BRAF V600E and KRAS G12S mutations in sporadic schwannomas, particularly in the head and neck, including VS. The primary aim of this study was to assess the frequency of BRAF and KRAS activating mutations in sporadic, unilateral VS at the cerebellopontine angle (CPA). A secondary aim was to determine whether these mutations are identified in other CPA tumors in the differential diagnosis of VS.
Design: CPA and CPA region tumors, as well as meningiomas with prominent fibroblastic histology, were identified in the electronic medical record. Clinical history, as well as radiology and pathology reports, were reviewed to exclude patients with NF1/ NF2. For selected cases, paraffin blocks were pulled and slides reviewed to verify the presence of sufficient tumor. Pyrosequencing (PS) of BRAF (exon 15, codon 600) and KRAS (exon 2, codons 12 and 13) was performed following PCR of DNA isolated from representative tissue sections.
Results: Eleven unilateral VSs (mean age 51.2 years, 7 males) and eleven comparison cases (mean age 54.1 years, 4 males) were identified. Comparison cases consisted of nine meningiomas (4 CPA, 6 with fibroblastic histology, 2 WHO Grade II) and two infratentorial hemangiopericytomas (WHO Grade II). No KRAS mutations were identified. Two cases demonstrated BRAF codon 600 T>A sequence changes at or just above (3 and 4 % in a single VS and hemangiopericytoma, respectively) the analytical sensitivity threshold of our clinical PS assay (set at 3%).
Conclusions: Very low levels of mutant BRAF sequence were identified in two cases (1 VS, 1 hemangiopericytoma), possibly representing a minor clone in these cases. These changes, potentially detectable by PS, would be below the detection of typical Sanger sequencing methods. Moreover, KRAS codon 12 or 13 mutations were not identified. Thus, recently reported BRAF and KRAS mutations in sporadic VSs are likely to be very rare events and likely noncontributory in the differential of CPA tumors. Alternate mechanisms to Ras-MAPK signaling pathway activation, or other pathways of oncogenesis, may be more common in sporadic non-syndromic VS.
Category: Neuropathology

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 248, Wednesday Afternoon


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