Sabina Zurac 1, P. J. Slootweg 2
1 Department of Pathology, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania
2 Department of Pathology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands
Abstract
Clear cell (CC) variants of odontogenic tumors have bland morphology and may be diffi cult to diagnose especially in small biopsies. We address our study to mitotic index in benign and malignant odontogenic tumors as criterion for diff erential diagnosis. We reviewed 14 cases of odontogenic carcinomas (“malignant group” including 6 CC odontogenic carcinomas (CCOC), 6 ameloblastic carcinomas (AC) and 2 primary intraosseous squamous cell carcinoma (PISCC)) and 30 cases of ameloblastoma with clear cell component (“benign group”). We compared the mitotic index of the benign group versus the malignant group; the mitoses were counted in consecutive high power fi elds (hpfs) without necrosis or stromal deposition and the mitotic index was reported as number of mitoses per 10 hpfs. Th e statistical calculations were performed using EXCEL and EPIINFO programs. Th e mitotic index was lower in benign tumors (most benign cases had less than 20 mitoses / 10 hpfs) but almost half of the odontogenic carcinomas had similar mitotic count. Th ere is no statistical signifi cance of higher mitotic index in malignant tumors compared to benign ones (P = 0,057). Th ere was also a tendency towards higher number of mitoses in solid / multicystic ameloblastoma than in desmoplastic variant. Frank malignant tumors present strikingly numerous mitoses; otherwise, ordinary ameloblastomas may reveal an impressive number of mitoses, sometimes in such a proportion that the examiner could be induced to consider that certain tumor as being malignant. Unfortunately, in daily practice, the main problem is not represented by high mitotic index in ameloblastoma but by low mitotic index in CCOC. An odontogenic tumor with clear cells may present a reduced number of mitoses but the overall behavior (destruction of the cortical bone, invasion in the soft tissue or even metastases) may allow its classifi cation as malignant. When dealing with an individual case, mitotic index is not a reliable parameter for diff erentiating benign ameloblastomas from odontogenic carcinomas since many ameloblastomas may have an increased number of mitoses while CCOC may show a not very prominent mitotic activity.