Ameloblastoma is a locally destructive and invasive tumour that can recur despite adequate surgical removal. Molecular studies have offered interesting findings regarding ameloblastoma pathogenesis. In the present review, the following topics are discussed regarding its molecular nature: clonality, cell cycle proliferation, apoptosis, tumour suppressor genes, ameloblastin and other enamel matrix proteins, osteoclastic mechanism and matrix metalloproteinases and other signalling molecules. It is clear from the literature reviewed that translational studies are necessary to identify prognostic markers of ameloblastoma behaviour and to establish new diagnostic tools to the differential diagnosis of unicystic from multicystic ameloblastoma. Finally, molecular biology studies are also important to develop more effective alternative approaches to the treatment of this aggressive odontogenic tumour.
Letter to the editor Recurrent KRAS G12V pathogenic mutation in adenomatoid odontogenic tumours Dear Editor, The adenomatoid odontogenic tumour (AOT) is a non-aggressive encapsulated tumour, being usually diagnosed in association with an unerupted permanent maxillary canine [1,2]. There are scarce reports of multiple AOTs [3-5] and a patient with Schimmelpenning syndrome (SS) with AOT was reported [6]. SS is characterized by sebaceous nevi, associated with ipsilateral abnormalities of the central nervous system, resulting from postzygotic autosomal dominant HRAS or KRAS lethal mutations that survive by somatic mosaicism [7]. RAS mutations were previously reported in lesional tissue (including nevus sebaceous) of a patient, but not in normal skin or blood leukocytes, consistent with a somatic mosaicism [7]. We evaluated one AOT sample from a SS patient having multiple AOTs (index patient) and two sporadic AOTs (samples #1 and #2) for mutations in a panel of 50 oncogenes and tumour suppressor genes, including RAS family, by using Ion AmpliSeq TM Cancer Hotspot Panel v2 (Life Technologies, Carlsbad, USA). After filtering by missense variants, candidate variants from the panel were defined as those pathogenic variants in regions with a depth greater than X500 and frequency greater than 5%. Only KRASc.35G > T (KRASG12V) fit this criteria, and was validated by TaqMan Ò Mutation Detection Assay using the probes KRAS_476_mu and KRAS_rf (Applied Biosystems, Foster City, USA). We further interrogated the KRASG12V mutation in six extra AOTs (samples #3-8) by the TaqMan Ò Assay. This KRAS mutation was detected in the three samples, as well as in four (samples #3, #4, #5 and #7) out of six additional samples. The mutation was validated by Sanger sequencing (Fig. 1). No other pathogenic mutation interrogated was detected. Blood leukocytes from the index patient were negative for KRASG12V mutation. To determine the specificity of the KRASG12V mutation in the context of odontogenic tumours, we evaluated three ameloblastomas, two dentinogenic ghost cell tumours and two normal oral mucosa samples using the TaqMan Ò Assay, being all negative for the mutation. Constitutively activation of the MAPK pathway by BRAFV600E mutation was reported in ameloblastoma [8-10], and in ameloblastic carcinoma [11]. We describe a recurrent oncogenic mutation in an upstream activator of MAPK, KRAS, in AOT. RAS mutations are found in 30% of human cancers and 80% of KRAS mutations occur at codon 12, being highly frequent in lung adenocarcinoma, pancreatic and colon carcinomas [12]. In our series, seven out of nine AOTs exhibited the KRASG12V mutation. The KRAS mutation was identified in the index patient sample and in sporadic AOTs, a candidate to driver mutation in these lesions. Driver mutations confer growth advantage to tumour cells and are positively selected during cancer evolution [13].
Odontogenic myxoma (OM) is a benign odontogenic neoplasm that tends to recur due to bone infiltration. This review focuses on the molecular aspects of the OM. The following topics are discussed: clonal nature, matrix metalloproteinases, apoptosis and cell proliferation, genetic alterations, and other markers. Translational studies are necessary to identify the prognostic markers of this lesion, and also, molecular biology studies may help to identify the etiologic factors and to develop more effective and less aggressive approaches, other than surgery, to the treatment of this infiltrating odontogenic tumor.
Central giant cell lesion (CGCL) and peripheral giant cell lesion (PGCL) of the jaws are characterized by multinucleated osteoclast-like giant cells in a background of mononuclear cells. While mononuclear cells retain proliferative activity in both lesions, giant cells are Ki-67 negative. This observation raised the theory that giant cells are formed by cytoplasmic fusion of mononuclear cells, and also that these lesions are of reactive nature. As the giant cells are not proliferating in CGCL and PGCL, apoptosis of such cells should be investigated. We investigated the transcription of BAX and BCL-2 mRNAs in six fresh samples of CGCL and six fresh samples of PGCL by qRT-PCR (quantitative reverse transcription PCR) and used immunohistochemistry to demonstrate the localization of these proteins, as well as caspase 3 active in six paraffin-embedded samples of CGCL and nine paraffin-embedded samples of PGCL. While both groups showed increased expression of BAX and BCL-2 mRNA, PGCL showed a higher apoptotic index (ratio BAX/BCL-2) than CGCL. The three proteins investigated were expressed almost exclusively in the cytoplasm of giant cells. To further confirm apoptotic activity, we performed TUNEL analysis in the same samples of the immunohistochemistry and found a higher positivity in the giant cells of PGCL compared to the giant cells of CGCL. Our results show increased expression of apoptotic-related genes in both PGCL and CGCL and that the giant cells are probably the main source of these events. Also, it raises a hypothesis that differences in the apoptotic activity might be associated with the different clinical behavior of CGCL and PGCL.
Abstract.A variety of diseases of the jaws may present multinucleated giant cells. These diseases include central giant cell lesions (CGCL), peripheral giant cell lesions (PGCL), brown tumor of hyperparathyroidism (BTH), and cherubism. The multinucleated giant cells in these lesions are osteoclast-like. Since NFATc1 plays a significant role in osteoclast differentiation, the present study aimed to compare the expression of NFATc1 in CGCL, PGCL, BTH and cherubism. A total of 14 formalin-fixed and paraffin-embedded tissue samples of CGCL (n=4), PGCL (n=5), BTH (n=3) and cherubism (n=2) were included in the study. An immunohistochemical analysis was performed to investigate the NFATc1 protein.The majority of giant cells in all of the cases were positive for nuclear NFATc1 and the immunostaining pattern was similar in all of the groups. Although our study supports the hypothesis that giant cell accumulation in PGCL, CGCL, BTH and cherubism is mediated by NFATc1, functional studies are required to investigate this hypothesis.
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