The landscape of genetic alterations in ameloblastomas relates to clinical features

Factors Associated with Recurrence of Ameloblastoma: A Scoping Review

PURPOSE

This scoping review aimed to identify factors associated with the recurrence of ameloblastoma.

METHODS

Systematic searches were conducted in PubMed, Scopus, and EMBASE, based on the board research question: "What factors are related to the recurrence of ameloblastoma?". English-language observational studies addressing the risk and preventive factors associated with recurrent ameloblastoma were included and data were extracted.

RESULTS

Eighty-three retrospective observational studies met the inclusion criteria. The identified prognostic factors for recurrence included: (1) Tumor size/diameter/volume, (2) cortical bone perforation/ soft tissue invasion, (3) multilocular radiolucency, (4) impacted tooth-involving lesions, (5) root resorption, (6) WHO classification - conventional (solid/multicystic) ameloblastoma, (7) histological subtype - mural invasion of unicystic ameloblastoma, (8) conservative treatment modalities - simple enucleation, curettage, and marsupialization, and (9) non-extraction/preservation of involved teeth. No strong evidence linked immunohistochemical expression to recurrence. Interestingly, BRAF p.V600E remained controversial in terms of recurrence, despite being a frequent finding in ameloblastoma.

CONCLUSION

Certain clinical characteristics, radiographic findings, histological subtypes, and treatment choices of ameloblastoma can help identify patients at high risk of recurrence. Further prospective studies to evaluate the prognostic factor model and research on immunohistochemistry are required.

Anti-MAPK Targeted Therapy for Ameloblastoma: Case Report with a Systematic Review

Ameloblastoma, a benign yet aggressive odontogenic tumor known for its recurrence and the severe morbidity from radical surgeries, may benefit from advancements in targeted therapy. We present a case of a 15-year-old girl with ameloblastoma successfully treated with targeted therapy and review the literature with this question: Is anti-MAPK targeted therapy safe and effective for treating ameloblastoma? This systematic review was registered in PROSPERO, adhered to PRISMA guidelines, and searched multiple databases up to December 2023, identifying 13 relevant studies out of 647 records, covering 23 patients treated with MAPK inhibitor therapies. The results were promising as nearly all patients showed a positive treatment response, with four achieving complete radiological remission and others showing substantial reductions in primary, recurrent, and metastatic ameloblastoma sizes. Side effects were mostly mild to moderate. This study presents anti-MAPK therapy as a significant shift from invasive surgical treatments, potentially enhancing life quality and clinical outcomes by offering a less invasive yet effective treatment alternative. This approach could signify a breakthrough in managing this challenging tumor, emphasizing the need for further research into molecular-targeted therapies.

Molecular pathogenesis of ameloblastoma

Ameloblastoma (AM) is a benign, although aggressive, epithelial odontogenic tumour originating from tooth-forming tissues or remnants. Its aetiopathogenesis remains unclear; however, molecular analysis techniques have allowed researchers to progress in understanding its genetic basis. The high frequency of BRAF p.V600E as a main driver mutation in AM is well established; nevertheless, it is insufficient to explain its tumourigenesis. In this review, we aimed to integrate the current knowledge about the biology of AM and to describe the main genetic alterations reported, focusing on the findings of large-scale sequencing and gene expression profiling techniques. Current evidence shows that besides BRAF mutation and activation of the MAPK pathway, alterations in Hedgehog and Wnt/β-catenin pathway-related genes are also involved in AM pathogenesis. Recently, a tumour suppressor gene, KMT2D, has been reported as mutated by different research groups. The biological impact of these mutations in the pathogenesis of AM has yet to be elucidated. Further studies are needed to clarify the impact of these findings in the identification of novel biomarkers that could be useful for diagnosing, classifying, and molecular targeting this neoplasm.

Association of MDM2 Overexpression in Ameloblastomas with MDM2 Amplification and BRAFV600E Expression

Ameloblastoma is a rare tumor but represents the most common odontogenic neoplasm. It is localized in the jaws and, although it is a benign, slow-growing tumor, it has an aggressive local behavior and high recurrence rate. Therefore, alternative treatment options or complementary to surgery have been evaluated, with the most promising one among them being a targeted therapy with the v-Raf murine sarcoma viral oncogene homologue B (BRAF), as in ameloblastoma the activating mutation V600E in BRAF is common. Studies in other tumors have shown that the synchronous inhibition of BRAF and human murine double minute 2 homologue (MDM2 or HDM2) protein is more effective than BRAF monotherapy, particularly in the presence of wild type p53 (WTp53). To investigate the MDM2 protein expression and gene amplification in ameloblastoma, in association with BRAFV600E and p53 expression. Forty-four cases of ameloblastoma fixed in 10% buffered formalin and embedded in paraffin were examined for MDM2 overexpression and BRAFV600E and p53 expression by immunohistochemistry, and for MDM2 ploidy with fluorescence in situ hybridization. Sixteen of forty-four (36.36%) cases of ameloblastoma showed MDM2 overexpression. Seven of sixteen MDM2-positive ameloblastomas (43.75%) were BRAFV600E positive and fifteen of sixteen MDM2-positive ameloblastomas (93.75%) were p53 negative. All MDM2 overexpressing tumors did not show copy number alterations for MDM2. Overexpression of MDM2 in ameloblastomas is not associated with MDM2 amplification, but most probably with MAPK activation and WTp53 expression. Further verification of those findings could form the basis for the use of MDM2 expression as a marker of MAPK activation in ameloblastomas and the trial of dual BRAF/MDM2 inhibition in the management of MDM2-overexpressing/BRAFV600E-positive/WTp53 ameloblastomas.

Clinicoradiologic features of ameloblastomas: A single-centre study of 155 cases

BACKGROUND

The purpose of the current study was to report on the clinical presentation and radiologic features of 155 cases of ameloblastoma (AB), representing a detailed, large, single-centre radiologic study.

METHODS

Histologically confirmed cases were reviewed over 11 years. Demographic and clinical data were retrieved from the patient's records. Radiologic information was analysed from available radiographs. The radiologic features of ABs were assessed according to the mean age of presentation and the mean duration of the lesion. The distinguishing radiologic features between adults/children and sex were also evaluated.

RESULTS

A statistically significant correlation existed between loss of border demarcation and advanced mean age. Multilocular lesions were markedly more common in adults compared to children. Multilocular ABs were associated with increased lesion duration and advanced mean age. Radiologic signs of reactive bony changes associated with the tumour presented at the highest mean duration of all bony effects. Bony expansion and cortical destruction were statistically correlated with lesion duration. Tooth impaction was more common in children. Some mandibular lesions reached a significant size, resulting in impingement of the maxillary sinus, zygoma, orbit and pterygoid plates.

CONCLUSION

Due to unfortunate healthcare access constraints, ABs grow to significant sizes and exhibit features not often reported in the literature. The findings of this analysis highlighted the radiologic features of ABs expressed through the mean age and duration of the lesion. This emphasises the significance of timely management of these lesions.

Efficiency of B-RAF-/MEK-inhibitors in B-RAF mutated Ameloblastoma: Case report and review of literature

Background

Ameloblastoma is a benign but locally invasive and aggressive odontogenic tumor harboring activating BRAF V600E mutations in about two thirds of the cases.

Case presentation

Neoadjuvant therapy with Dabrafenib and Trametinib was given to a 42-year-old male patient with recurrent ameloblastoma of the right mandible with a BRAF V600E mutation for 18 months. The patient manifested an excellent response to the therapy with remarkable reduction in tumor size from 72.6 mm to 55.9 mm. Histopathologically, the tumor underwent significant degenerative changes with only a few sparse vital residuals revealing 0 % Ki67 proliferative index.

Conclusions

Neoadjuvant therapy with BRAF-inhibitors or BRAF-MEK-inhibitors is an effective means to reduce the size of mandibulary ameloblastomas. We propose the consideration of neoadjuvant therapy in future treatment modalities to minimize post-surgical morbidity and facial deformations.

Pediatric Odontogenic Tumors

Odontogenic tumors are rare tumors of the jaws that arise from remnants of the tooth forming apparatus. Some odontogenic tumors demonstrate strong predilection for pediatric patients including the unicystic ameloblastoma, adenomatoid odontogenic tumor, ameloblastic fibroma, ameloblastic fibro-odontoma, odontoma, and primordial odontogenic tumor. In this review, we discuss the clinical, radiographic, histopathologic, and molecular characteristics of select odontogenic tumors that demonstrate pediatric predilection and review management.

The Role of BRAF Inhibitors in the Management of Ameloblastoma: A Literature Review

Ameloblastoma is one of the most prevalent but enigmatic benign odontogenic tumors of the jaw, accounting for approximately 10% of all maxillary and mandibular tumors. This neoplasia is distinguished by exhibiting several clinical and histological variants along with several mutations that affect its behavior. The ameloblastoma treatment plan is determined by the tumor's size, anatomical location, histologic variant, and anatomical involvement. On chromosome 7, there is a proto-oncogene called BRAF. When BRAF is mutated, it becomes an oncogene and continuously produces proteins like MEK and ERK, members of mitogen-activated protein kinase (MAPK). In the signaling pathway, these proteins activate transcription factor inside the nucleus that helps in cell division and growth. Numerous neoplasms have been linked to more than 40 BRAF mutations. The most common one is BRAF proto-oncogene serine/threonine kinase (BRAF) V600E, whose treatment has been linked to a positive outcome. BRAF inhibitors like vemurafenib, dabrafenib, and sorafenib have shown excellent results, especially in metastatic ameloblastoma. BRAF, particularly in the case of metastatic ameloblastoma, inhibitors such as vemurafenib, dabrafenib, and sorafenib, has demonstrated outstanding results. Targeted therapies have been employed as adjuvant therapies to enhance cosmetic outcomes, even though no reports of serial cases demonstrate their effectiveness in ameloblastomas. In the treatment of ameloblastomas, the identification of BRAF V600E and additional mutations as the prime targeted therapies has proven to be a significant breakthrough where surgical treatment was contraindicated. In this article, we review the presence of BRAF V600E mutations, their inhibitors, and targeted therapies in ameloblastoma.

Genomic profiling and precision medicine in complex ameloblastoma

BACKGROUND

Ameloblastoma may present a significant treatment challenge in the locally advanced, recurrent and metastatic setting. Comprehensive genomic profiling (CGP) can identify targetable genomic alterations to aid in treatment.

METHODS

Ameloblastoma samples were sequenced using hybrid-capture based sequencing. A systematic literature review was performed to examine outcomes in studies employing targeted treatment in ameloblastoma.

RESULTS

We reviewed 14 cases of Ameloblastoma using CGP. There were six patients with activating BRAF mutations, five with PIK3CA, five with SMO, four with FGFR2, one with EGFR, and one with ROS1. All cases were MSI stable and the median TMB was 2.5 mutations/Mb. A separate literature review of clinical outcomes in ameloblastoma showed a predominance of at least partial response to targeted treatment (7/12 cases).

CONCLUSION

CGP is helpful in identifying specific driver mutations in patients with complex ameloblastoma. Targeted treatment has been employed with success in achieving treatment response.

BRAF V600E Mutation in Ameloblastoma: A Systematic Review and Meta-Analysis

The discovery that ameloblastoma has a high mutation incidence of BRAF V600E may enable a better investigation of pathophysiology. However, there is inconsistent evidence regarding this mutation occurrence and its association with clinical information. This systematic review and meta-analysis aim to pool the overall mutation prevalence of BRAF V600E in reported ameloblastoma cases and to determine its association with patient demographic and clinicopathological features. Following the PRISMA guidelines, a comprehensive article search was conducted through four databases (Scopus, Google Scholar, PubMed, and Web of Science). Seventeen articles between 2014 and 2022 met the inclusion criteria with 833 ameloblastoma cases. For each included study, the significance of BRAF V600E on the outcome parameters was determined using odd ratios and 95% confidence intervals. Meta-analysis prevalence of BRAF V600E in ameloblastoma was 70.49%, and a significant meta-analysis association was reported for those younger than 54 years old and in the mandible. On the contrary, other factors, such as sex, histological variants, and recurrence, were insignificant. As a result of the significant outcome of BRAF V600E mutation in ameloblastoma pathogenesis, targeted therapy formulation can be developed with this handful of evidence.

Adenoid ameloblastoma harbors beta-catenin mutations

Adenoid ameloblastoma is a very rare benign epithelial odontogenic tumor characterized microscopically by epithelium resembling conventional ameloblastoma, with additional duct-like structures, epithelial whorls, and cribriform architecture. Dentinoid deposits, clusters of clear cells, and ghost-cell keratinization may also be present. These tumors do not harbor BRAF or KRAS mutations and their molecular basis appears distinct from conventional ameloblastoma but remains unknown. We assessed CTNNB1 (beta-catenin) exon 3 mutations in a cohort of 11 samples of adenoid ameloblastomas from 9 patients. Two of the 9 patients were female and 7 male and in 7/9 patients the tumors occurred in the maxilla. Tumors of 4 of these 9 patients harbored CTNNB1 mutations, specifically p.Ser33Cys, p.Gly34Arg, and p.Ser37Phe. Notably, for one patient 3 samples were analyzed including the primary tumour and two consecutive recurrences, and results were positive for the mutation in all three tumors. Therefore, 6/11 samples tested positive for the mutation. In the 6 mutation-positive samples, ghost cells were present in only 2/6, indicating beta-catenin mutations are not always revealed by ghost cell formation. Dentinoid matrix deposition was observed in 5/6 mutation-positive samples and clear cells in all 6 cases. None of the cases harbored either BRAF or KRAS mutations. Beta-catenin immunoexpression was assessed in the samples of 8 patients. Except for one wild-type case, all cases showed focal nuclear expression irrespective of the mutational status. Together with the absence of BRAF mutation, the detection of beta-catenin mutation in adenoid ameloblastomas supports its classification as a separate entity, and not as a subtype of ameloblastoma. The presence of this mutation may help in the diagnosis of challenging cases.

The diagnostic utility of BRAF VE1 mutation-specific immunohistochemistry in ameloblastoma

Ameloblastoma is a benign, locally aggressive odontogenic neoplasm with variable solid and cystic morphology. On account of its histologic variety, diagnostically challenging cases can bear resemblance to odontogenic keratocyst/keratocystic odontogenic tumor (KCOT) or dentigerous cyst (DC). BRAF^V600E mutation has been reported to be specific for and frequent in ameloblastoma, and this study evaluated the usefulness of immunohistochemistry (IHC) using the BRAF VE1 mutant-specific antibody as a diagnostic adjunct in this setting. We investigated 46 ameloblastomas, 30 KCOTs, and 30 DCs. BRAF VE1 IHC was performed on all cases and allele-specific polymerase chain reaction (AS-PCR) for BRAF^V600E mutation was performed on 30 ameloblastomas and any IHC-positive KCOT/DC. BRAF VE1 IHC was positive in 31/37 (83.8%) mandibular ameloblastomas but not in any maxillary ameloblastomas (0/9), KCOT (0/30), or DC (0/30). Equivocal staining was seen in 1/37 (3.3%) mandibular ameloblastomas. Of the 30 ameloblastomas subjected to AS-PCR, BRAF^V600E mutation was identified in 19/23 (82.6%) mandibular ameloblastomas and 0/7 (0.0%) maxillary ameloblastomas. BRAF^V600E mutant ameloblastomas were positive by IHC in 18/19 (94.7%) cases and equivocal in 1/19 (5.3%) cases. All 11 (100.0%) BRAF-wild type ameloblastomas were negative by IHC. BRAF VE1 is an excellent tool for the diagnosis of mandibular ameloblastoma but of limited utility in the maxilla, where it less commonly occurs and where BRAF^V600E mutation is considerably less frequent.

Ameloblastoma: An Updated Narrative Review of an Enigmatic Tumor

Ameloblastoma is one of the most common benign odontogenic tumors of the jaw that constitutes about 10% of all tumors that arise in the mandible and maxilla. It is a slow-growing but locally invasive tumor that presents with painless swelling of the mandible or maxilla. The World Health Organization (WHO) classification of 2017 describes ameloblastomas of the following four types: ameloblastoma; unicystic ameloblastoma; extraosseous/peripheral ameloblastoma; and metastasizing ameloblastoma. The diagnosis of ameloblastoma requires computerized tomography (CT) imaging as well as a biopsy. A biopsy is helpful in differentiating ameloblastoma from ossifying fibroma, osteomyelitis, giant cell tumor, cystic fibrous dysplasia, myeloma, and sarcoma. The best treatment of ameloblastoma is aggressive en bloc resection with simultaneous reconstruction. The high recurrence rate and large tissue defects have been long-standing issues in the treatment of ameloblastoma. Recent molecular developments strongly suggest the possibility of targeted therapy with better outcomes in ameloblastomas. We present a detailed updated narrative review of our current understanding and management of this enigmatic tumor.

Phase II Study of Copanlisib in Patients With Tumors With PIK3CA Mutations: Results From the NCI-MATCH ECOG-ACRIN Trial (EAY131) Subprotocol Z1F

PURPOSE

Activating mutations in PIK3CA are observed across multiple tumor types. The NCI-MATCH (EAY131) is a tumor-agnostic platform trial that enrolls patients to targeted therapies on the basis of matching genomic alterations. Arm Z1F evaluated copanlisib, an α and δ isoform-specific phosphoinositide 3-kinase (PI3K) inhibitor, in patients with PIK3CA mutations (with or without PTEN loss).

PATIENTS AND METHODS

Patients received copanlisib (60 mg intravenous) once weekly on days 1, 8, and 15 in 28-day cycles until progression or toxicity. Patients with KRAS mutations, human epidermal growth factor receptor 2-positive breast cancers, and lymphomas were excluded. The primary end point was centrally assessed objective response rate (ORR); secondary end points included progression-free survival, 6-month progression-free survival, and overall survival.

RESULTS

Thirty-five patients were enrolled, and 25 patients were included in the primary efficacy analysis as prespecified in the Protocol. Multiple histologies were enrolled, with gynecologic (n = 6) and gastrointestinal (n = 6) being the most common. Sixty-eight percent of patients had ≥ 3 lines of prior therapy. The ORR was 16% (4 of 25, 90% CI, 6 to 33) with P = .0341 against a null rate of 5%. The most common reason for protocol discontinuation was disease progression (n = 17, 68%). Grade 3/4 toxicities observed were consistent with reported toxicities for PI3K pathway inhibition. Sixteen patients (53%) had grade 3 toxicities, and one patient (3%) had grade 4 toxicity (CTCAE v5.0). Most common toxicities include hyperglycemia (n = 19), fatigue (n = 12), diarrhea (n = 11), hypertension (n = 10), and nausea (n = 10).

CONCLUSION

The study met its primary end point with an ORR of 16% (P = .0341) with copanlisib showing clinical activity in select tumors with PIK3CA mutation in the refractory setting.

Identification of BRAF V600E mutation in odontogenic tumors by high-performance MALDI-TOF analysis

Odontogenic tumors are rare lesions with unknown etiopathogenesis. Most of them are benign, but local aggressiveness, infiltrative potential, and high recurrence rate characterize some entities. The MAP-kinase pathway activation can represent a primary critical event in odontogenic tumorigenesis. Especially, the BRAF V600E mutation has been involved in 80–90% of ameloblastic lesions, offering a biological rationale for developing new targeted therapies. The study aims to evaluate the BRAF V600E mutation in odontogenic lesions, comparing three different detection methods and focusing on the Sequenom MassARRAY System. 81 surgical samples of odontogenic lesions were subjected to immunohistochemical analysis, Sanger Sequencing, and Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry (Sequenom). The BRAF V600E mutation was revealed only in ameloblastoma samples. Moreover, the presence of BRAF V600E was significantly associated with the mandibular site (ρ = 0.627; P value <0.001) and the unicystic histotype (ρ = 0.299, P value <0.001). However, any significant difference of 10-years disease-free survival time was not revealed. Finally, Sequenom showed to be a 100% sensitive and 98.1% specific, suggesting its high-performance diagnostic accuracy. These results suggest the MAP-kinase pathway could contribute to ameloblastic tumorigenesis. Moreover, they could indicate the anatomical specificity of the driving mutations of mandibular ameloblastomas, providing a biological rational for developing new targeted therapies. Finally, the high diagnostic accuracy of Sequenom was confirmed.

The Molecular Pathology of Odontogenic Tumors: Expanding the Spectrum of MAPK Pathway Driven Tumors

Odontogenic tumors comprise a heterogeneous group of lesions that arise from the odontogenic apparatus and their remnants. Although the etiopathogenesis of most odontogenic tumors remains unclear, there have been some advances, recently, in the understanding of the genetic basis of specific odontogenic tumors. The mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) pathway is intimately involved in the regulation of important cellular functions, and it is commonly deregulated in several human neoplasms. Molecular analysis performed by different techniques, including direct sequencing, next-generation sequencing, and allele-specific qPCR, have uncovered mutations in genes related to the oncogenic MAPK/ERK signaling pathway in odontogenic tumors. Genetic mutations in this pathway genes have been reported in epithelial and mixed odontogenic tumors, in addition to odontogenic carcinomas and sarcomas. Notably, B-Raf proto-oncogene serine/threonine kinase (BRAF) and KRAS proto-oncogene GTPase (KRAS) pathogenic mutations have been reported in a high proportion of ameloblastomas and adenomatoid odontogenic tumors, respectively. In line with the reports about other neoplasms that harbor a malignant counterpart, the frequency of BRAF p.V600E mutation is higher in ameloblastoma (64% in conventional, 81% in unicystic, and 63% in peripheral) than in ameloblastic carcinoma (35%). The objective of this study was to review MAPK/ERK genetic mutations in benign and malignant odontogenic tumors. Additionally, such genetic alterations were discussed in the context of tumorigenesis, clinical behavior, classification, and future perspectives regarding therapeutic approaches.

Genetic Profile of Adenomatoid Odontogenic Tumor and Ameloblastoma. A Systematic Review

Purpose: To perform a comprehensive and systematic critical appraisal of the genetic alterations reported to be present in adenomatoid odontogenic tumor (AOT) compared to ameloblastoma (AM), to aid in the understanding in their development and different behavior.

Methods: An electronic search was conducted in PubMed, Scopus, and Web of Science during March 2021. Eligibility criteria included publications on humans which included genetic analysis of AOT or AM.

Results: A total of 43 articles reporting 59 AOTs and 680 AMs were included. Different genomic techniques were used, including whole-exome sequencing, direct sequencing, targeted next-generation sequencing panels and TaqMan allele-specific qPCR. Somatic mutations affecting KRAS were identified in 75.9% of all AOTs, mainly G12V; whereas a 71% of the AMs harbored BRAF mutations, mainly V600E.

Conclusions: The available genetic data reports that AOTs and AM harbor somatic mutations in well-known oncogenes, being KRAS G12V/R and BRAFV600E mutations the most common, respectively. The relatively high frequency of ameloblastoma compared to other odontogenic tumors, such as AOT, has facilitated the performance of different sequencing techniques, allowing the discovery of different mutational signatures. On the contrary, the low frequency of AOTs is an important limitation for this. The number of studies that have a assessed the genetic landscape of AOT is still very limited, not providing enough evidence to draw a conclusion regarding the relationship between the genomic alterations and its clinical behavior. Thus, the presence of other mutational signatures with clinical impact, co-occurring with background KRAS mutations or in wild-type KRAS cases, cannot be ruled out. Since BRAF and RAS are in the same MAPK pathway, it is interesting that ameloblastomas, frequently associated with BRAFV600E mutation have aggressive clinical behavior, but in contrast, AOTs, frequently associated with RAS mutations have indolent behavior. Functional studies might be required to solve this question.

Genetic Study of BRAF V600E and SMO L412F Mutations in Japanese Patients with Ameloblastoma

Background and aim: Ameloblastoma is a benign, intraosseous, progressively growing, epithelial, odontogenic neoplasm. BRAF and SMO mutations have been reported in ameloblastoma. In this study, we evaluated BRAF V600E and SMO L412F mutations; and assessed the relationship between BRAF V600E mutant expression and the clinicopathological features in Japanese patients with ameloblastoma. Methods: We examined 24 formalin-fixed paraffin-embedded samples. All specimens were from patients with mandibular ameloblastoma: 20 were conventional ameloblastoma and 4 were unicystic ameloblastoma. The BRAF V600E mutation was assessed by Sanger sequencing and immunohistochemistry, and the SMO L412F mutation was assessed only by Sanger sequencing. Results: Twenty of the 24 (83%) ameloblastoma samples carried the BRAF V600E mutation; 22 of the 24 (92%) samples were immunohistochemically positive for BRAF V600E. However, the SMO L412F mutation was not detected in any of them. The BRAF V600E mutation status did not correlate with the clinicopathological features, such as age, sex, location, method, recurrence, and subtype. Conclusion: BRAF inhibitors could be a potential treatment option for Japanese patients with ameloblastoma, harboring the BRAF V600E mutation.

Molecular diagnostics in odontogenic tumors

BACKGROUND

Odontogenic tumors (OTs) are rare, with an estimated incidence rate of less than 0.5 cases per 100,000 per year. The causes of OTs remain unclear. Nonetheless, the majority of OTs seem to arise de novo, without an apparent causative factor. Although the etiopathogenesis of most OTs remains unclear, there have been some recent advances in understanding the genetic basis relating to specific histologies and clinical features. Molecular analyses performed by different techniques, including Sanger sequencing, next-generation sequencing, and allele-specific PCR, have uncovered mutations in genes related to the oncogenic MAPK/ERK signaling pathway. Genetic mutations in these pathway genes have been reported in epithelial and mixed OTs, in addition to odontogenic carcinomas and sarcomas. Notably, B‑RAF proto-oncogene serine/threonine kinase (BRAF) and KRAS proto-oncogene GTPase (KRAS) pathogenic mutations have been reported in a high proportion of ameloblastoma and ameloblastoma-related tumors and adenomatoid odontogenic tumors, respectively.

OBJECTIVE

To discuss how molecular profiling aids in diagnostic classification of odontogenic tumors.

CONCLUSION

Molecular profiling of odontogenic tumors helps to identify patients for neoadjuvant therapies and reduces postoperative morbidity.

Correlation of BRAF mutational status with clinical characteristics and survival outcomes of patients with ameloblastoma: the experience of 11 Italian centres

AIMS

Ameloblastoma is a rare odontogenic tumour with an aggressive local behaviour. Mutations in the mitogen-activated protein kinase pathway, namely BRAF V600E mutations, are a common finding. To date, there is no clear correlation between BRAF V600 mutation and clinical outcome.

METHODS

We retrospectively reviewed the medical records of patients who underwent surgery for ameloblastoma between May 1998 and June 2018, at 11 participating Italian centres. BRAF mutational status was evaluated by quantitative PCR/pyrosequencing. The primary end points were to determine BRAF mutational status in primitive and recurrent ameloblastoma, and to assess the relapse-free interval (RFI); the secondary end point was to investigate the correlation of BRAF mutational status with the clinical features of the tumour and survival outcomes.

RESULTS

Overall, 74 patients were included: 33 (44.5%) were BRAF wild type and 41 (55.4%) BRAF V600 mutated. BRAF V600 mutated ameloblastomas occurred more frequently in younger patients (p=0.0031), were located at the mandible (p=0.0009) and presented with unicystic variant. After a median follow-up of 60 months, 21 (28.3%) patients relapsed (30.3% and 26.8% in the BRAF wild type and BRAF mutated group, respectively). At univariable Cox models, none of the investigated variables, including microscopic margin involvement, was associated with RFI.

CONCLUSIONS

Local recurrence occurs in 30% of patients with ameloblastoma. BRAFV600 mutation is associated with younger age, mandibular localisation and with unicystic ameloblastoma. Neither BRAF mutation nor microscopically positive surgical margins were associated with RFI. Further studies are needed to elucidate outcomes of this rare disease according to clinical, histopathological and comprehensive molecular features.

Identification of circ_0089153/miR-608/EGFR p53 axis in ameloblastoma via MAPK signaling pathway

OBJECTIVES

This study investigated the role of circular RNAs (circRNAs) in the pathogenesis of ameloblastoma (AB), identifying potential novel targets for future targeted therapy.

MATERIALS AND METHODS

CircRNA and microRNA (miRNA) profiling in AB were built with microarrays. Six novel circRNAs were validated, circ-miRNA networks were delineated. Hsa-miR-608 was filtered over cross-comparison between database screening, miRNA microarray and validated. Circ-miRNA binding sponge was validated via luciferase reporter assay. Downstream mRNAs were screened. Regulation between miRNAs and mRNAs was confirmed in vitro. Gene interaction networks and circRNA-miRNA-mRNA interaction pathway enrichment analyses were established.

RESULTS

Six differentially expressed circRNAs were selected and validated. According to miRNAs and pathways predicted, six correlated miRNAs were selected, hsa-miR-608 was filtered and validated. The hsa_circ_0089153/hsa-miR-608 binding sponge was validated. Downstream gene interaction networks showed that EGFR and p53 had the strongest co-expression. In vitro transfection results confirmed the suppressive function of miR-608 and EGFR p53. Hsa_circ_0089153/hsa-miR-608/EGFR p53 interaction pathway enrichment analysis confirmed functions mainly enriched in MAPK and related signaling pathways regulating AB progression.

CONCLUSIONS

Six novel circRNAs were identified. Hsa_circ_0089153/hsa-miR-608 sponging was validated, hsa-miR-608 downregulated EGFR and p53, which might further regulate cell proliferation, differentiation, apoptosis, and cell cycle processes via the MAPK signaling pathway.

Conceptual changes in ameloblastoma: Suggested re-classification of a "veteran" tumor

OBJECTIVES

The merging of ameloblastoma (AM) with mural unicystic ameloblastoma (UAM-M) was suggested by the 2017 WHO based on similar treatment needs. In an international multicenter study, we investigated the characteristics of their merged product (merged-AM) and raised the possibility of unifying AM and UAM (total-AM).

MATERIALS AND METHODS

AM and UAM (luminal/intraluminal/mural), separate and combined, were analyzed for demographic/clinical/radiological features. ANOVA and chi-square tests were followed by univariate and multivariate analyses, and significance was set at p < .05.

RESULTS

The patients' mean age was 39.6 ± 20.3 years in merged-AM (147 AM, 76 UAM-M), 45.1 ± 19.4 years in AM (p = .009). Merged-AM comprised 51.3% multilocular/48.7% unilocular tumors, AM comprised 72.5%/27.5%, respectively (p < .001). Merged-AM was associated with impacted teeth in 30.8%, AM in 18% (p = .023). The probability of merged-AM for multilocularity increased by 2.4% per year of age (95%CI 0.6-4.2, p = .009). Association with impacted teeth decreased by 7.9% per year of age (95%CI 1.9-14.39, p = .009). Merged-AM did not differ from total-AM (p > .05).

CONCLUSIONS

Merged-AM partially differed from AM, but differences appeared to diminish in an age/time-wise manner. Merged-AM and total-AM were nearly indistinguishable. Therefore, AM and UAM may be considered a continuous spectrum of one type of tumor, further necessitating revision of the treatment approaches.

Genetic factors in the pathogenesis of ameloblastoma, dentigerous cyst and odontogenic keratocyst

Ameloblastoma (AB), dentigerous cyst (DC) and Odontogenic keratocyst (OKC) are odontogenic lesions with propensity to malignant transformation or local invasion. The molecular mechanisms of development of these lesions are not fully understood. However, some researches have reported dysregulation of tumor suppressor genes or oncogenes in these lesions. Down-regulation of P53 gene has been reported in AB, DC and OKC. Moreover, several long non-coding RNAs such as ENST00000512916 and KIAA0125 have been dysregulated in AB tissues. Single nucleotide polymorphisms within a variety of genes have been associated with certain types of odontogenic lesions. In the current review, we summarize the current data about the expression pattern of genes in these lesions and the observed association between genetic polymorphisms and development of these lesions.

Ameloblastoma: A succinct review of the classification, genetic understanding and novel molecular targeted therapies

Ameloblastomas are benign but locally invasive neoplasms which may grow to massive proportions and cause significant morbidity. Although some types of ameloblastoma can be treated predictably with aggressive surgical treatment, recurrent ameloblastoma and metastasising ameloblastoma are still difficult to treat. Recent studies have identified recurrent somatic and activating mutations in the mitogen-activated protein kinase (MAPK) and sonic hedgehog (SHH) signalling pathways in ameloblastoma. This development provided a possibility that molecular targeted therapies can be used as neoadjuvant treatment. In this review, we provide a summary of the latest WHO classification of ameloblastoma, the current understanding of genetic mutations and novel molecular targeted therapies arising from the recent developments.

High frequency of BRAF V600E mutation in Iranian population ameloblastomas

Background

Ameloblastoma is a common locally invasive but slow-growing neoplasm of the jaws with an odontogenic origin. Association between BRAF V600E mutation and clinicopathologic features and behavior of ameloblastoma remains controversial. This study aimed to evaluate BRAF V600E gene mutation and expression of its related proteins with clinicopathologic parameters in conventional ameloblastoma.

Material and Methods

50 Formalin-fixed paraffin-embedded blocks were included in this study. Immunohistochemistry was done using rabbit monoclonal BRAF V600E mutation-specific antibody VE1. Quantitative real-time polymerase chain reaction assay was used for evaluating of BRAF V600E mutation.

Results

Expression of BRAF V600E antibody was Positive in 42 out of 50 cases (84%). 46 (92%) out of 50 specimens showed BRAF V600E mutation. There were 13 cases of recurrence (26%). 3 out of 4 cases with negative mutations did not show recurrence.

Conclusions

We report the highest frequency (92%) of BRAF V600E mutation in ameloblastomas in the Iranian population. Although there was not a significant association between BRAF V600E‑positive immunoexpression and recurrence and clinicopathologic parameters, its high frequency could emphasize its role as a therapeutic marker in the future.

Key words:Conventional ameloblastoma, BRAF V600E, recurrence.

DNA damage and repair scenario in ameloblastoma

Ameloblastoma is a rare human disease of benign neoplasm odontogenic tumor with a lower prevalence but higher recurrence rate. Etiology of ameloblastoma is not fully understood thus lacks implementation of curative treatments. One of the proposed models of evolution of ameloblastoma is related to alteration in DNA damage and repair effects. Growing body of literature has associated defect in DNA damage and repair mechanisms with cancer risk and various adverse health outcomes in humans. Persistent defect of repair and escape of these genomic unstable cells from cell death mechanisms can contribute towards accumulation of oncogene driver or tumor suppressor mutations selective for malignant transformations. In addition, growth, progression and survival of tumor depends upon its DNA repair mechanisms too, thus identifying a DNA repair biomarker can be of advantageous to eliminate the tumor. Understanding the interconnection of oral lesion and role of various DNA repair mechanisms in context to ameloblastoma will assist to build up a platform for translational based research. This study is a literature review of research work published up to date in the field of ameloblastoma in regard to DNA damage and repair effects.

Mutational spectrum of acquired resistance to reversible versus irreversible EGFR tyrosine kinase inhibitors

Background

Over the past years, EGFR tyrosine kinase inhibitors (TKI) revolutionized treatment response. 1st-generation (reversible) EGFR TKI and later the 2nd –generation irreversible EGFR TKI Afatinib were aimed to improve treatment response. Nevertheless, diverse resistance mechanisms develop within the first year of therapy. Here, we evaluate the prevalence of acquired resistance mechanisms towards reversible and irreversible EGFR TKI.

Methods

Rebiopsies of patients after progression to EGFR TKI therapy (> 6 months) were targeted to histological and molecular analysis. Multiplexed targeted sequencing (NGS) was conducted to identify acquired resistance mutations (e.g. EGFR p.T790M). Further, Fluorescence in situ hybridisation (FISH) was applied to investigate the status of bypass mechanisms like, MET or HER2 amplification.

Results

One hundred twenty-three rebiopsy samples of patients that underwent first-line EGFR TKI therapy (PFS ≥6 months) were histologically and molecularly profiled upon clinical progression. The EGFR p.T790M mutation is the major mechanism of acquired resistance in patients treated with reversible as well as irreversible EGFR TKI. Nevertheless a statistically significant difference for the acquisition of T790M mutation has been identified: 45% of afatinib- vs 65% of reversible EGFR TKI treated patients developed a T790M mutation (p-value 0.02). Progression free survival (PFS) was comparable in patients treated with irreversible EGFR irrespective of the sensitising primary mutation or the acquisition of p.T790M.

Conclusions

The EGFR p.T790M mutation is the most prominent mechanism of resistance to reversible and irreversible EGFR TKI therapy. Nevertheless there is a statistically significant difference of p.T790M acquisition between the two types of TKI, which might be of importance for clinical therapy decision.

LGR5+ epithelial tumor stem-like cells generate a 3D-organoid model for ameloblastoma

Ameloblastoma (AM) is a benign but locally aggressive tumor with high recurrences. Currently, underlying pathophysiology remains elusive, and radical surgery remains the most definitive treatment with severe morbidities. We have recently reported that AM harbors a subpopulation of tumor epithelial stem-like cells (AM-EpiSCs). Herein, we explored whether LGR5⁺ epithelial cells in AM possess stem-like cell properties and their potential contribution to pathogenesis and recurrence of AM. We found that LGR5 and stem cell-related genes were co-expressed in a subpopulation of AM epithelial cells both in vivo and in vitro, which were enriched under 3D-spheroid culture. As compared to LGR5⁻ counterparts, LGR5⁺ AM epithelial cells showed increased expression of various EMT- and stemness-related genes, and functionally, exhibited increased capacity to form 3D-spheroids and generate human tumor 3D organoids, which recapitulated the histopathologic features of distinct subtypes of solid AM, thus, contributing a useful human tumor platform for targeted therapeutic screening. Treatment with a selective BRAF^V600E inhibitor, vemurafenib, unexpectedly enriched the subpopulation of LGR5⁺ AM-EpiSCs in tumor 3D organoids, which may have explained therapeutic resistances and recurrences. These findings suggest that LGR5⁺ AM-EpiSCs play a pivotal role in pathogenesis and progression of AM and targeted inhibition of both BRAF and LGR5 potentially serves a novel nonsurgical adjuvant therapeutic approach for this aggressively benign jaw tumor.

Ameloblastic fibrosarcoma: clinicopathological and molecular analysis of seven cases highlighting frequent BRAF and occasional NRAS mutations

AIMS

Ameloblastic fibrosarcoma (AFS) is an aggressive odontogenic neoplasm featuring malignant mesenchymal stroma in addition to an ameloblastic epithelial component, and is hence considered to be the malignant counterpart of ameloblastic fibroma (AF). AFS is exceedingly rare, with <110 cases having been reported so far. Although BRAF mutations are recognised driver mutations in ameloblastoma, the molecular pathogenesis of AFS remains elusive.

METHODS AND RESULTS

We herein describe seven AFSs that were analysed, for the first time, for mutations in the BRAF-NRAS pathway. The patients were four females and three males aged 23-57 years (median, 26 years). Three tumours developed after one or multiple recurrences of AF (4-20 years after initial diagnosis), two showed transition from AF-like bland areas, and two developed de novo. All patients were treated with surgery; adjuvant chemotherapy was given to one patient. At the last follow-up, five patients were alive and well (19-344 months). The remainder were lost to follow-up. Histological examination showed variable sarcomatous overgrowth with varying degrees of atypia and increased mitotic activity. The epithelial component varied greatly according to the degree of sarcomatous overgrowth. Molecular testing revealed BRAF V600E mutations in five cases and NRAS p.Gln61Lys mutation in one case. One tumour was wild-type.

CONCLUSION

To our knowledge, this is the first study on BRAF/NRAS mutations in AFS. Given the activity of RAF and MEK inhibitors across different cancers harbouring V600E mutations, our data strongly suggest that all AFS cases should be genetically tested, and that targeted treatment approaches for this extremely rare sarcoma subtype should be clinically investigated.

Discovery of novel molecular characteristics and cellular biological properties in ameloblastoma

Ameloblastoma is a rare odontogenic benign tumor accounting for less than 1% of head and neck tumors. Advanced next generation sequencing (NGS) analyses identified high frequency of BRAF V600E and SMO L412F mutations in ameloblastoma. Despite the existence of whole genomic sequence information from patients with ameloblastoma, entire molecular signature of and the characteristics of ameloblastoma cells are still obscure. In this study, we sought to uncover the molecular basis of ameloblastoma and to determine the cellular phenotype of ameloblastoma cells with BRAF mutations. Our comparative cDNA microarray analysis and gene set enrichment analysis (GSEA) showed that ameloblastoma exhibited a distinct gene expression pattern from the normal tissues: KRAS-responsive gene set is significantly activated in ameloblastoma. Importantly, insulin like growth factor 2 (IGF2), a member of KRAS-responsive genes, enhances the proliferation of an ameloblastoma cell line AMU-AM1 with BRAF mutation. In addition, Toll-like receptor 2 (TLR2) knockdown readily inactivated KRAS-responsive gene sets as well as increases caspase activities, suggesting that TLR2 signaling may mediate cell survival signaling in ameloblastoma cells. Collectively, the findings may help to further clarify the pathophysiology of ameloblastoma and lead to the development of precision medicine for patients with ameloblastoma.

Ameloblastoma with mucous cells: A clinicopathological, BRAF mutation, and MAML2 rearrangement study

OBJECTIVES

To investigate the clinicopathological features, BRAF V600E mutation, and MAML2 rearrangement of ameloblastoma with mucous cell differentiation.

MATERIALS AND METHODS

Five cases of ameloblastoma with mucous cell differentiation were retrospectively studied. Clinicopathological features, BRAF V600E mutation, and MAML2 rearrangement were analyzed. Follow-up information was available for all cases.

RESULTS

Of five cases, two cases were male and three were female, aged 18-55 years. Four cases were located in the mandible and one case in the maxilla. Histologically, four of the five cases (80%) presented with cystic features and three of the five cases (60%) with varying degrees of squamous metaplasia. The mucous cells were located in the epithelial islands or the luminal aspect of the cystic cavities. The BRAF V600E mutation was found in three of five cases (60%). All the cases showed no MAML2 rearrangement. Two cases were recurrent lesions, and one case had a local recurrence during the follow-up.

CONCLUSIONS

Ameloblastoma with mucous cell differentiation is closely related to the cystic features, squamous metaplasia, and shows a high prevalence of BRAF V600E mutation. The absence of MAML2 rearrangement reveals that ameloblastoma with mucous cell differentiation and central mucoepidermoid carcinoma (MEC) are two distinct tumor entities.

A review of the molecular profile of benign and malignant odontogenic lesions

Odontogenic cysts and tumors are heterogeneous lesions, originating from elements or remnants of the odontogenic apparatus. Although the majority of these lesions are benign and never undergo malignant transformation, rare malignant tumors may arise de novo or from benign precursors. The molecular basis of these lesions is still poorly understood. This article summarizes and discusses studies using small, medium, and large-scale and/or "-omic" techniques to describe the molecular characteristics of benign and malignant odontogenic lesions and briefly debates strategies to increase the use of "-omic" and multi-omic approaches or integrative analyses in the research of these lesions. A comprehensive understanding of the molecular aspects of odontogenic lesions by using large-scale approaches will enable us to refine the classification of this heterogeneous group of disorders and provide more accurate biomarkers for precise diagnosis, prognosis, and development of molecular tools in the management of patients with these conditions.

Current concepts in ameloblastoma-targeted therapies in B-raf proto-oncogene serine/threonine kinase V600E mutation: Systematic review

BACKGROUND

Ameloblastomas are common benign epithelial odontogenic neoplasms that present an aggressive and unpredictable behavior that may modify treatment strategies. Different signaling pathways that participate in the progression of these tumors have been identified. B-raf proto-oncogene serine/threonine kinase (BRAF) is a protein involved in the behavior of ameloblastomas, and it is related to many cell mechanisms. BRAF gene mutations have been identified in ameloblastomas, of which the BRAF V600E (valine substituted by glutamic acid at amino acid 600) mutation has been the most common and can be present concomitantly with other mutations that may be involved in its behavior. Targeted therapies have been used as an alternative in the case of resistance or contraindications to conventional treatments.

AIM

To document the presence of BRAF V600E and additional mutations, their behavior, and targeted therapies in these tumors.

METHODS

An electronic literature search was conducted according to PRISMA guidelines in PubMed/MEDLINE, Cochrane, EMBASE, and SpringerLink using the terms “ameloblastomas”, “BRAF V600E”, “additional mutations”, and “targeted therapies”. Ameloblastomas were classified according to WHO guidelines. Inclusion criteria were articles in English, published not more than 10 years ago, and studies with laboratory works related to BRAF V600E. Articles were evaluated by two independent reviewers and retrieved for full-text evaluation. The EBLIP Critical Appraisal Checklist was used to evaluate the quality of the eligible studies. Descriptive statistical analysis was performed.

RESULTS

Two independent reviewers, with a substantial concordance indicated by a kappa coefficient of k = 0.76, evaluated a total of 19 articles that were included in this study. The analysis registered 521 conventional ameloblastomas (AM), 81 unicystic ameloblastomas (UA), 13 ameloblastic carcinomas (AC), three metastatic ameloblastomas (MA), and six peripheral ameloblastomas (PA), of which the histopathological type, anatomic location, laboratory tests, expression of BRAF mutation, and additional mutations were registered. The BRAF V600E mutation was found in 297 AM (57%), 63 UA (77.7%), 3 AC (23%), 1 MA (50%), and 5 PA (83.3%). Follicular type predominated with a total of 116 cases (40%), followed by plexiform type with 63 cases (22.1%). Furthermore, both types presented additional mutations, in which alterations in JAK3 P132T, SMARCB1, PIK3CA, CTNNB1, SMO, and BRAF G606E genes were found. Four case reports were found with targeted therapy to BRAF V600E.

CONCLUSION

The identification of BRAF V600E and additional mutations as an aid in targeted therapies has been a breakthrough in alternative treatments of ameloblastomas where surgical treatments are contraindicated.

An immunohistochemical and genetic study of BRAFV600E 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 (BRAF^V600E ). We examined specimens from 32 Japanese patients to detect the prevalence of the BRAF^V600E mutation, and to evaluate the relationship between immunohistochemical (IHC) expression and genetic results, of BRAF^V600E+ ameloblastoma. Among the 32 cases, 22 (69%) were IHC positive for BRAF^V600E protein, and 10 (31%) were IHC negative; and polymerase chain reaction showed 16 of 21 tested cases (76%) carried the BRAF^V600E mutation. Our findings indicate that that samples that stain IHC positive for BRAF^V600E protein are more likely to carry the BRAF^V600E mutation. These results support assessments for BRAF mutations, and the use of BRAF inhibitors as targeted therapy for ameloblastoma in Japanese patients.

Conservative management is effective in unicystic ameloblastoma occurring from the neonatal period: A case report and a literature review

Unicystic ameloblastoma (UA), a benign odontogenic tumor of the jaw, represents less than a third of all ameloblastomas and seems less aggressive than other types of ameloblastoma. We present here the first case of UA that developed prenatally and was successfully managed in the early neonatal period with marsupialization and curettage performed carefully to avoid injury to the tooth germ. BRAF and SMO mutations were not detected. After 2 years of follow-up, complete reossification and normal eruption of deciduous teeth were noted, and there was no recurrence of UA. We recommend conservative treatment of UA in the pediatric population to avoid loss of and/or injury to the tooth germ, provided close follow-up is carried out all through the individual's growth for early detection of potential recurrences, growth impairments, or tooth eruption disorders. The intratumoral somatic mutational status of BRAF, SMO, RAS family, and FGFR2 may help determine personalized targeted treatment, particularly in case of recurrence.

[BRAF gene mutations in ameloblastic fibromas]

OBJECTIVE

To investigate the BRAF gene mutations in ameloblastic fibroma (AF), and to further analyze the relationship between the BRAF mutation and clinical characteristics so as to provide new reference to the study of AF's molecular pathology.

METHODS

Sixteen cases diagnosed as AF at the Department of Oral Pathology, Peking University School of Stomatology between January 1990 and December 2017 were collected. Genomic DNA was extracted from formalin-fixed, paraffin embedded tissues using the QIAamp DNA Mini Kit (Qiagen, Germany) according to the manufacturer's instructions. Polymerase chain reaction (PCR) and direct sequencings were used to detect the BRAF gene mutations. The clinicopathological data, such as the age, location of the lesion, symptoms and treatments were retrospectively analyzed.

RESULTS

The sixteen cases of AF involved nine women and seven men aged 2-67 years. Three lesions occurred in the maxilla and thirteen in the mandible. The most common presenting symptom of AF was a painless slowly enlarging mass with swelling. Ten patients received conservative treatment and the other six patients received radical surgery. Three cases relapsed during the study period. BRAF gene mutation was found in sixteen of all the sixteen samples analyzed (100%). The BRAF mutation was a point mutation with a thymine-adenine transversion at nucleotide 1 799 of 15 exons, resulting in a change at residue 600 that substituted glutamine for valine. This mutation was the strongest activator of the downstream RAS/RAF/MEK/ERK-MAPK signaling pathway. This helped to bring about a gain-of-function mutation due to a V600E substitution. Many studies identified that BRAF regulated survival, apoptosis, and proliferation of cells by inducing MAPK pathways activation. For the existing cases, none of the age, sex, location, recurrence and treatments had a statistically significant correlation with BRAF mutation.

CONCLUSION

Our findings demonstrated high prevalence of BRAF V600E mutation in AF. The pathogenic role remains to be clarified．.

Update on Odontogenic Tumors: Proceedings of the North American Head and Neck Pathology Society

Odontogenic tumors are rare entities, often derived from the epithelial remnants in the gnathic bones following odontogenesis. This brief manuscript will seek to address recent developments pertaining to odontogenic tumors as well as particularly uncommon odontogenic tumors and the difficulties in their diagnosis.

Advancements in MAPK signaling pathways and MAPK-targeted therapies for ameloblastoma: A review

Numerous signal transduction pathways are closely associated with the occurrence, development, and prognosis of ameloblastoma (AM). Mitogen-activated protein kinase (MAPK) is a serine/threonine-specific protein kinase that transduces intracellular signals in critical cellular phenomena. A number of recent analyses have reported that the MAPK signaling pathway contributes significantly to AM. High-throughput DNA sequencing methods, such as next-generation sequencing using Illumina have yielded advancements in studies on MAPK signaling pathways and their association with AM; in particular, BRAF V600E is mediated by the activation of the Ras/Raf/MAPK pathway. This review discusses advancements in studies on MAPK signaling pathways and MAPK-targeted inhibitors or antibodies, along with the merits and demerits of MAPK-targeted therapies, finally followed by a discussion regarding more efficient potential MAPK-targeted therapies to treat AM with few side effects, thereby providing novel insights into targeted therapy for AM.

Overcoming EGFRG724S-mediated osimertinib resistance through unique binding characteristics of second-generation EGFR inhibitors

The emergence of acquired resistance against targeted drugs remains a major clinical challenge in lung adenocarcinoma patients. In a subgroup of these patients we identified an association between selection of EGFR^T790M-negative but EGFR^G724S-positive subclones and osimertinib resistance. We demonstrate that EGFR^G724S limits the activity of third-generation EGFR inhibitors both in vitro and in vivo. Structural analyses and computational modeling indicate that EGFR^G724S mutations may induce a conformation of the glycine-rich loop, which is incompatible with the binding of third-generation TKIs. Systematic inhibitor screening and in-depth kinetic profiling validate these findings and show that second-generation EGFR inhibitors retain kinase affinity and overcome EGFR^G724S-mediated resistance. In the case of afatinib this profile translates into a robust reduction of colony formation and tumor growth of EGFR^G724S-driven cells. Our data provide a mechanistic basis for the osimertinib-induced selection of EGFR^G724S-mutant clones and a rationale to treat these patients with clinically approved second-generation EGFR inhibitors.

Acquired resistance to targeted drugs remains a major clinical challenge in lung adenocarcinoma patients. Here, the authors show how the acquired EGFR^G724S mutation induces resistance to third-generation EGFR inhibitors and why the mutant kinase remains susceptible to second-generation inhibitors.

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

Background

Ameloblastoma is a slow-growing neoplasm of the jaw, for which the standard treatment is surgical removal of the lesion with high recurrence rates and elevated morbidity. Systemic therapy is not established in the literature.

Case presentation

We present a case of a 29-year-old woman diagnosed with an ameloblastoma of the left mandible who had been subjected to several surgical procedures over twenty years due to multiple local recurrences. Molecular testing revealed a BRAF V600E mutation, and vemurafenib was started. She experienced complete resolution of symptoms related to the disease, and image scans evidenced continuous shrinkage of the neoplastic lesion after eleven months of therapy.

Conclusion

This is the first report showing clinical benefit and radiological response with vemrafenib for recurrent ameloblastoma. Targeted therapy addressing BRAF V600E mutation has the potential to change clinical practice of this rare disease.