Utility of BRAF V600E immunohistochemistry in the diagnosis of mandibular ameloblastomas.

Ameloblastoma, odontogenic keratocyst (OKC), and dentigerous cyst (DC) can have similar radiographic and histological appearances. The purpose of this study was to determine the utility of BRAF immunohistochemistry in discerning mandibular ameloblastomas from OKCs and DCs. This retrospective cohort study included patients treated between 1998 and 2018. Inclusion criteria include incisional biopsy-proven mandibular ameloblastoma, OKC, or DC, and sufficient tissue for immunohistochemistry. The primary predictor variable was the type of lesion. The primary outcome variable was the presence/absence of BRAF V600E immunoreactivity. The cohort consisted of 43 patients (19 female, 24 male; mean age 48 ± 17 years). There were 22 ameloblastomas, 11 OKCs, and 10 DCs. Among ameloblastomas, 68.2% (15/22) stained positive for BRAF V600E; no OKC or DC was positive (P < 0.001). By subtype, the majority of the follicular (83.3%), unicystic (83.3%), desmoplastic (66.7%), and acanthomatous (100%) subtypes were positive, but only 33.3% of the plexiform subtype were positive. BRAF immunohistochemistry may be a useful adjunct in the differentiation of ameloblastoma from OKCs and DCs on incisional biopsies. It may be particularly useful for small samples with a prominent cystic component or equivocal histopathology. Mandibular lesions that are BRAF immunohistochemistry positive are unlikely to be DCs or OKCs.

Ji YD ，Johnson DN ，Faquin WC ，Peacock ZS ... -  《-》

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). BRAFV600E 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 BRAFV600E 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, BRAFV600E mutation was identified in 19/23 (82.6%) mandibular ameloblastomas and 0/7 (0.0%) maxillary ameloblastomas. BRAFV600E 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 BRAFV600E mutation is considerably less frequent.

Mendez LD ，Wolsefer NS ，Asa SL ，Wasman J ，Yoest JM ，Stojanov IJ ... -  《-》

The BRAF p.V600E mutation is a common event in ameloblastomas but is absent in odontogenic keratocysts.

Odontogenic keratocysts (OKCs) are jaw lesions with a tendency to recur. PTCH1 gene mutations are common events in most OKCs; however, other genetic alterations underlying OKC pathogenesis have not yet been elucidated. BRAF p.V600E mutations have recently been detected in some odontogenic tumors, such as ameloblastoma and ameloblastic fibroma, although their involvement in OKC is still unclear. In this study we aimed to clarify the presence and/or frequency of BRAF p.V600E mutations in OKCs. Thirty-five cases of OKCs, 13 of which were associated with Gorlin syndrome, were evaluated for BRAF p.V600E mutations by direct sequencing of the formalin-fixed, paraffin-embedded, and frozen tissue samples. Seventeen cases of ameloblastoma and six cases of dentinogenic ghost cell tumor were also included in this study for comparative purposes. BRAF p.V600E mutations were not detected in any of the OKCs or dentinogenic ghost cell tumors. In contrast, 14 of 17 cases of ameloblastoma (82.35%) were proven to harbor BRAF p.V600E mutations. BRAF p.V600E mutations were common in ameloblastomas, as previously reported, but were absent in OKCs and dentinogenic ghost cell tumors. These results further confirmed the noninvolvement of BRAF in OKCs and suggested different pathogenic mechanisms involved in various odontogenic lesions.

Zhang R ，Yang Q ，Qu J ，Hong Y ，Liu P ，Li T ... -  《-》

BRAF p.V600E status in epithelial areas of ameloblastoma with different histological aspects: Implications to the clinical practice.

BRAF p.V600E is reported in up to 80% of ameloblastomas. Despite the high frequency, the presence of this mutation in different histopathological areas of the tumour has not been investigated. This information has an important role in the use of BRAF p.V600E assessment as an auxiliary tool in the differential diagnosis between unicystic ameloblastoma and other odontogenic cystic lesions, especially when only incisional biopsies are available. Therefore, the purpose of the present study was to investigate BRAF p.V600E heterogeneity in unicystic ameloblastoma. Five cases of ameloblastoma and two dentigerous cysts were analysed. The regions exhibiting different microscopic characteristics were selected from each ameloblastoma case and manually dissected. TaqMan allele-specific qPCR or Sanger sequencing was performed to determine BRAF p.V600E status. We screened the mutation in a small cohort of UA and no molecular heterogeneity was found. Four cases of ameloblastoma (80%) exhibited BRAF p.V600E in all different areas evaluated. One case did not harbour the mutation in any microscopic region analysed. The BRAF mutation was absent in the dentigerous cysts. Ameloblastomas appear to exhibit a homogeneous profile regarding the BRAF p.V600E no matter what histological feature is observed under light microscopy, suggesting that this molecular test may contribute to establish the correct diagnosis in cases microscopically resembling other odontogenic lesions.

Sant'Ana MSP ，Dos Santos Costa SF ，da Silva MP ，Martins-Chaves RR ，Pereira TDSF ，de Oliveira EM ，Martínez Pedraza R ，de Castro WH ，Gomes CC ，Gomez RS ，Fonseca FP ... -  《-》

BRAFV600E mutation in the diagnosis of unicystic ameloblastoma.

Unicystic ameloblastoma, an odontogenic neoplasm, presents clinical and radiographic similarities with dentigerous and radicular cysts, non-neoplastic lesions. It is not always possible to reach a final diagnosis with the incisional biopsy, leading to inappropriate treatment. The BRAFV600E activating mutation has been reported in a high proportion of ameloblastomas. The purpose of the study was to assess the utility of the detection of the BRAFV600E mutation in the differential diagnosis of unicystic ameloblastoma with dentigerous and radicular cysts. Twenty-six archival samples were included, comprising eight unicystic ameloblastomas (UAs), nine dentigerous and nine radicular cysts. The mutation was assessed in all samples by anti-BRAFV600E (clone VE1) immunohistochemistry (IHC) and by TaqMan mutation detection qPCR assay. Sanger sequencing was further carried out when samples showed conflicting results in the IHC and qPCR. Although all UAs (8/8) showed positive uniform BRAFV600E staining along the epithelial lining length, the mutation was not confirmed by qPCR and Sanger sequencing in three samples. Positive staining for the BRAFV600E protein was observed in one dentigerous cyst, but it was not confirmed by the molecular methods. Furthermore, 2/9 dentigerous cysts and 2/9 radicular cysts showed non-specific immunostaining of the epithelium or plasma cells. None of the dentigerous or radicular cysts cases presented the BRAFV600E mutation in the qPCR assay. The BRAFV600E antibody (clone VE1) IHC may show non-specific staining, but molecular assays may be useful for the diagnosis of unicystic ameloblastoma, in conjunction with clinical, radiological and histopathological features.

Pereira NB ，Pereira KM ，Coura BP ，Diniz MG ，de Castro WH ，Gomes CC ，Gomez RS ... -  《-》