High frequency of BRAF V600E mutations in ameloblastoma.

Ameloblastoma is a benign but locally infiltrative odontogenic neoplasm. Although ameloblastomas rarely metastasise, recurrences together with radical surgery often result in facial deformity and significant morbidity. Development of non-invasive therapies has been precluded by a lack of understanding of the molecular background of ameloblastoma pathogenesis. When addressing the role of ERBB receptors as potential new targets for ameloblastoma, we discovered significant EGFR over-expression in clinical samples using real-time RT-PCR, but observed variable sensitivity of novel primary ameloblastoma cells to EGFR-targeted drugs in vitro. In the quest for mutations downstream of EGFR that could explain this apparent discrepancy, Sanger sequencing revealed an oncogenic BRAF V600E mutation in the cell line resistant to EGFR inhibition. Further analysis of the clinical samples by Sanger sequencing and BRAF V600E-specific immunohistochemistry demonstrated a high frequency of BRAF V600E mutations (15 of 24 samples, 63%). These data provide novel insight into the poorly understood molecular pathogenesis of ameloblastoma and offer a rationale to test drugs targeting EGFR or mutant BRAF as novel therapies for ameloblastoma.

Kurppa KJ ，Catón J ，Morgan PR ，Ristimäki A ，Ruhin B ，Kellokoski J ，Elenius K ，Heikinheimo K ... -  《-》

Activating FGFR2-RAS-BRAF mutations in ameloblastoma.

Ameloblastoma is an odontogenic neoplasm whose overall mutational landscape has not been well characterized. We sought to characterize pathogenic mutations in ameloblastoma and their clinical and functional significance with an emphasis on the mitogen-activated protein kinase (MAPK) pathway. A total of 84 ameloblastomas and 40 non-ameloblastoma odontogenic tumors were evaluated with a combination of BRAF V600E allele-specific PCR, VE1 immunohistochemistry, the Ion AmpliSeq Cancer Hotspot Panel, and Sanger sequencing. Efficacy of a BRAF inhibitor was evaluated in an ameloblastoma-derived cell line. Somatic, activating, and mutually exclusive RAS-BRAF and FGFR2 mutations were identified in 88% of cases. Somatic mutations in SMO, CTNNB1, PIK3CA, and SMARCB1 were also identified. BRAF V600E was the most common mutation, found in 62% of ameloblastomas and in ameloblastic fibromas/fibrodentinomas but not in other odontogenic tumors. This mutation was associated with a younger age of onset, whereas BRAF wild-type cases arose more frequently in the maxilla and showed earlier recurrences. One hundred percent concordance was observed between VE1 immunohistochemistry and molecular detection of BRAF V600E mutations. Ameloblastoma cells demonstrated constitutive MAPK pathway activation in vitro. Proliferation and MAPK activation were potently inhibited by the BRAF inhibitor vemurafenib. Our findings suggest that activating FGFR2-RAS-BRAF mutations play a critical role in the pathogenesis of most cases of ameloblastoma. Somatic mutations in SMO, CTNNB1, PIK3CA, and SMARCB1 may function as secondary mutations. BRAF V600E mutations have both diagnostic and prognostic implications. In vitro response of ameloblastoma to a BRAF inhibitor suggests a potential role for targeted therapy.

Brown NA ，Rolland D ，McHugh JB ，Weigelin HC ，Zhao L ，Lim MS ，Elenitoba-Johnson KS ，Betz BL ... -  《-》

Progress towards personalized medicine for ameloblastoma.

Gomes CC ，Diniz MG ，Gomez RS 《-》

An immunohistochemical and genetic study of BRAF(V600E) mutation in Japanese patients with ameloblastoma.

Ameloblastoma is an odontogenic tumor of the jaw. It most frequently occurs in the mandible, and less often in the maxilla. Mandibular ameloblastoma harbors a BRAF mutation that causes a valine (V) to glutamic acid (E) substitution at codon 600 (BRAFV600E ). We examined specimens from 32 Japanese patients to detect the prevalence of the BRAFV600E mutation, and to evaluate the relationship between immunohistochemical (IHC) expression and genetic results, of BRAFV600E+ ameloblastoma. Among the 32 cases, 22 (69%) were IHC positive for BRAFV600E protein, and 10 (31%) were IHC negative; and polymerase chain reaction showed 16 of 21 tested cases (76%) carried the BRAFV600E mutation. Our findings indicate that that samples that stain IHC positive for BRAFV600E protein are more likely to carry the BRAFV600E mutation. These results support assessments for BRAF mutations, and the use of BRAF inhibitors as targeted therapy for ameloblastoma in Japanese patients.

Seki-Soda M ，Sano T ，Ito K ，Yokoo S ，Oyama T ... -  《-》

Clinical benefit and radiological response with BRAF inhibitor in a patient with recurrent ameloblastoma harboring V600E mutation.

Fernandes GS ，Girardi DM ，Bernardes JPG ，Fonseca FP ，Fregnani ER ... -  《BMC CANCER》