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Adenoid ameloblastoma harbors beta-catenin mutations

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Victor Coutinho Bastos, Bruna Pizziolo Coura, Letícia Martins Guimarães, Bianca Gomes Fernandes, Alexander Chak-Lam Chan, Pablo Agustin Vargas, Luciana Bastos-Rodrigues, Luiz Armando De Marco, John Hellstein, Selvam Thavaraj, John M Wright, Edward William Odell, Ricardo Santiago Gomez, Carolina Cavaliéri Gomes

Original languageEnglish
JournalModern pathology : an official journal of the United States and Canadian Academy of Pathology, Inc
Early online date15 Jul 2022
DOIs
Accepted/In press9 Jun 2022
E-pub ahead of print15 Jul 2022

Bibliographical note

Funding Information: The authors acknowledge the Centro de Aquisição e Processamento de Imagens (CAPI- ICB/UFMG) for the technical support in image acquisition. The authors are thankful for the support of the Research Support Foundation of the State of Minas Gerais (FAPEMIG), the National Council for Scientific and Technological Development (CNPq), and the Coordination for the Improvement of Higher Education Personnel (CAPES). VCB and LMG receive a CAPES scholarship. BPC, RSG, PAV, and CCG are research fellows at CNPq. Funding Information: The study was supported by the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) [REDE 0019-16, PPM-00022-17] and the National Council for Scientific and Technological Development (CNPq), Brazil. Publisher Copyright: © 2022, The Author(s), under exclusive licence to United States & Canadian Academy of Pathology.

King's Authors

Abstract

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.

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