Are Ameloblastic Fibroma-related Lesions True Tumors?: Evidence Through CNA and BRAF Mutation Analysis.

Abstract

Ameloblastic fibroma (AF) and related lesions, namely ameloblastic fibrodentinoma (AFD) and ameloblastic fibro-odontoma (AFO), span a spectrum from true neoplasms to hamartomas. The 2017 World Health Organization classification proposes that AFD and AFO are precursors to odontomas, yet their precise nature remains uncertain. This study examined 19 AF cases, 4 AFD, 15 AFO, 19 odontomas (OD, 14 complex, 5 compound), and 2 ameloblastic fibrosarcomas (AFS), focusing on clinical characteristics, recurrence, and molecular profiles. AF primarily affected individuals under 20 years (60.0% of cases), mainly in the mandible (68.4%), with a recurrence rate of 21.1% in the followed cases. AFD and AFO appeared in younger patients (average age 15.7 y) without any recurrence observed. Notable differences in site and size distribution were observed between AF, its related lesions, and odontomas. Copy number alterations (CNAs) were detected in the mesenchymal component in 9 of 19 AF (47.4%), 2 of 4 AFD (50.0%), 6 of 14 AFO (42.9%), and 2 of 2 AFS (100%). In contrast, all odontomas exhibited normal CNAs, highlighting the specificity of CNAs in mesenchymal elements of AF and related lesions. BRAF p.V600E mutation was identified in the mesenchymal component in 13 of 19 AF (68.4%), 2 of 4 AFD (50.0%), 8 of 15 AFO (53.3%), and 2 of 2 AFS (100%), whereas all 19 odontomas were BRAF wild type. No mutations were found in the epithelial component. Our analysis reveals that AF and its related lesions present a spectrum of biological behaviors, from true neoplasms to hamartomas. The presence of BRAF p.V600E mutations and CNAs in their mesenchymal components, as opposed to odontomas, indicates potential neoplastic characteristics. Profiling copy number alterations in AF and related lesions emerge as a valuable tool for enhancing their differential diagnosis and facilitating the anticipation of disease progression. Our findings underscore the efficacy of copy number alteration analysis in determining the nature of lesions within AF and related lesions.