Classic desmoplastic ameloblastoma : should it be a distinct subtype of ameloblastoma?-Based on clinicopathological, radiological, immunohistochemical and molecular study of a large cohort

Abstract

OBJECTIVES : To identify whether the classic desmoplastic ameloblastoma (DA) is an independent subtype of ameloblastoma. MATERIALS AND METHODS : Eighty-six classic DA and 28 hybrid DA cases were retrieved, and available clinical, radiological, and histopathological data were collected. DNA from microdissected tumor tissues were utilized for BRAF V600E, SMOL412F, and CTNNB1 mutation detection. Data of classic DA and hybrid DA were analyzed and compared with each other and with previous reports of conventional ameloblastoma (CA). RESULTS : 69.8% (60/86) of classic DA occurred in the mandible, with the majority affecting the anterior-premolar regions. They were characterized as osteolytic bone expansion (33.8 ± 12.8 mm) with internal bone/calcification (57/58, 98.3%) in radiology. Genetically, classic DA exhibited a high incidence of BRAF V600E mutation (58/62, 93.5%) but no CTNNB1 and SMO L412F mutations. Hybrid DA exhibited similarities to CA in jawbone location, tumor size, and radiology. The recurrence rate of classic DA (9.2%) was lower than that of CA (25.8%). CONCLUSION : High anterior-premolar distribution, a mixture of osteolytic and internal high-density shadows in radiology, smaller tumor size, compressed epithelium with abundant stroma and scattered bone, consistent mutation of BRAF V600E, and better prognosis all suggest that classic DA may be a distinct clinicopathological subtype of ameloblastoma.