Adenoid Ameloblastoma Shares Clinical, Histologic, and Molecular Features With Dentinogenic Ghost Cell Tumor: The Histologic Spectrum of WNT Pathway-Altered Benign Odontogenic Tumors

Calcifying Odontogenic Cyst Demonstrates Recurrent WNT Pathway Mutations and So-Called Adenoid Ameloblastoma-like Histology: Evidence Supporting Its Classification as a Neoplasm

Calcifying odontogenic cyst (COC), once called calcifying cystic odontogenic tumor (CCOT), is classified under the category of odontogenic cysts. However, the proliferative capacity of the lesional epithelium and consistent nuclear β-catenin expression raise questions about its current classification. This study aimed to determine whether COC would be better classified as a neoplasm in the histologic and molecular context. Eleven odontogenic lesions diagnosed as COC or CCOT were included in this study. The growth patterns of the lesional epithelium were analyzed histologically in all cases. β-catenin immunohistochemistry and molecular profiling using Sanger sequencing and whole-exome sequencing were performed in 10 cases. Of the 11 cases studied, histologic features reminiscent of so-called adenoid ameloblastoma were observed in 72.7% (8/11), and small islands of clear cells extended into the wall in 36.4% (4/11). Intraluminal and/or mural epithelial proliferation was found in 72.7% of the cases (8/11). Nuclear β-catenin expression was observed focally in all 10 cases studied, mainly highlighting epithelial cells forming morules and adjacent to dentinoid. CTNNB1 hotspot mutations were detected in 60.0% of the cases (6/10). All the remaining cases had frameshift mutations in tumor suppressor genes involved in the WNT pathway, including APC and NEDD4L. Recurrent WNT pathway mutations leading to nuclear translocation of β-catenin and distinct epithelial growth patterns found in COC are the neoplastic features shared by its solid counterpart, dentinogenic ghost cell tumor, supporting its classification as a tumor rather than a cyst.

Tumor immune microenvironment in odontogenic carcinomas: Evaluation of the therapeutic potential of immune checkpoint blockade

BACKGROUND

Despite recent advances in the use of immune checkpoint blockade (ICB) across various cancer types, its efficacy in odontogenic carcinomas remains unexplored. This study aims to investigate PD-L1 expression and the tumor immune microenvironment (TIME) in odontogenic carcinomas to determine the therapeutic potential of ICB and the significance of immune markers.

METHODS

The expressions of PD-L1 and T cell markers (CD3, CD8, and FOXP3) were visualized by immunohistochemistry in 21 tissue samples of odontogenic carcinomas. Tumoral PD-L1 expression and the density and spatial distribution of T cell subsets were evaluated, from which TIME was determined. The associations of the variables with clinicopathological and prognostic factors were statistically analyzed.

RESULTS

PD-L1 was positively expressed in 52.4% (11/21) of the cases studied. Among tumor types, ameloblastic carcinoma showed significantly higher PD-L1 expression (p = 0.016). TIME based on the intratumoral and stromal T cell distribution was immune-inflamed in 61.9% (13/21) and immune-excluded in 38.1% (8/21), with no immune-desert cases. PD-L1 expression was associated with the densities of all intratumoral T cell subsets (p = 0.03 for CD3, p = 0.03 for CD8, and p = 0.008 for FOXP3) but not with those of stromal T cells. High PD-L1 expression was associated with larger tumor size (p = 0.021), while the intratumoral CD8/CD3 ratio was inversely correlated with tumor size (p = 0.048).

CONCLUSION

These findings indicate the involvement of adaptive immune resistance in a subset of odontogenic carcinomas and support the therapeutic potential of ICB in patients with these rare malignancies.

Adenoid 'ameloblastoma': Clinicopathological description of 4 additional BRAF-negative cases

OBJECTIVE

Adenoid ameloblastoma (AA) is an epithelial odontogenic tumor that was recognized as a separate entity in the last odontogenic classification of WHO in 2022. The etiology is unknown, and the pathogenesis remains controversial. The objective of this study is to contribute the clinicopathological features of 4 additional BRAF-negative cases to the existing literature, aiming to enhance the molecular understanding of this unique tumor in the forthcoming classification.

MATERIALS AND METHODS

This study consists of a case series of four patients diagnosed with AA. The patients' demographic and clinical information were collected from the universities' medical achieves. Histopathologically, all cases were reexamined according to the latest update of the WHO odontogenic tumor classification. In addition to H&E and immunohistochemical stains, cytogenetics was also evaluated.

RESULTS

Well-defined unilocular radiolucent lesions were observed in all cases. Ameloblastoma-like components exhibited reserved nuclear polarity, suprabasal stellate reticulum-like epithelium, duct-like structure, whorls/morules, and cribriform architecture were common features. Variable immunoreactivity to CK7, CK19, CK14, p63, and p40 were determined, and proliferative activity was greater than 15%. The BRAF molecular study revealed no mutations.

CONCLUSIONS

When diagnosing AA, the essential histopathological characteristics must be rigorously applied, and a significant portion of the lesion should contain these features. Additionally, despite limited molecular data, since the BRAF mutation commonly observed in ameloblastomas is not present in the majority of AA cases, we propose changing the term "ameloblastoma" to "ameloblastic" and referring to it as "adenoid ameloblastic tumor" in the forthcoming classification.

Adenoid Ameloblastoma Shares Clinicopathologic, Immunohistochemical, and Molecular Features With Dentinogenic Ghost Cell Tumor: A Comparative Analysis

The updated classification of odontogenic tumors by the World Health Organization (WHO) has included adenoid ameloblastoma (AA) as a distinct entity. However, distinguishing between AA and dentinogenic ghost cell tumor (DGCT) can still be challenging due to their significant morphologic similarities. In this study, we aimed to compare the clinicopathologic, immunohistochemical, and molecular characteristics of AA and DGCT to aid in their differentiation and to shed light on their pathologic mechanisms. Thirteen cases of AA and 14 cases of DGCT (15 samples) were analyzed, along with 11 cases of adenomatoid odontogenic tumor (AOT) and 18 cases of conventional ameloblastoma (AM) for comparative purposes. The study found that AA and DGCT shared a similar long-term prognosis. Immunohistochemically, all cytokeratins detected, except CK8/18, were not statistically significant in differentiating AA and DGCT, while there was a statistically significant difference in the immunophenotype of CK7 and CK10/13 between AA and AM. Nuclear β-catenin accumulation were detected in all cases of AA and DGCT, while AOTs and AMs exhibited cytoplasmic β-catenin. Molecularly, CTNNB1 hotspot mutations were found in only 1 case of AA (1/13), but not found in the other 3 types of tumors. BRAF p.V600E mutation was positive in 2/13 (15%) AA, 1/15 (7%) DGCT, and 2/11 (18%) AOT cases. In comparison, conventional AM was positive for BRAF p.V600E mutation in 94% (17/18) of cases, while KRAS mutations were detected in 63% (7/11) of AOT cases. The study suggests that the so-called AA is a rare benign tumor that exhibits clinical, immunohistochemical, and molecular features similar to DGCTs. Based on these findings, AA should not be categorized as a standalone entity solely based on the presence of whorls/morules and cribriform/duct-like structures. Further studies are needed to investigate the pathologic mechanisms of these tumors and to identify potential therapeutic targets.

Infarction of basal cell adenoma of the parotid gland: First case report and literature review on CTNNB1 I35T mutations in salivary basal cell neoplasms

Infarction has rarely been reported in some types of salivary gland tumors. In this study, we present the first case of infarction occurring in salivary basal cell adenoma. A 62-year-old male presented with swelling in the left parotid region. Histopathological examination revealed extensive central necrosis surrounded by a rim of viable tumor tissue showing the typical histology of basal cell adenoma. Nuclear β-catenin expression and the CTNNB1 p.I35T (c.104 T > C) mutation were identified in the tumor. A diagnosis of basal cell adenoma with central necrosis was made, and the postoperative period was uneventful. In addition, we review the literature on CTNNB1 I35T mutations in basal cell neoplasms of the salivary glands. Awareness of the possible occurrence of infarction and the high frequency of the unique mutation in basal cell adenoma may help in the differential diagnosis of salivary gland tumors.

Ghost cell odontogenic carcinoma arising in dentinogenic ghost cell tumor, peripheral: A case report

Ghost cell odontogenic carcinoma (GCOC) is an extremely rare intraosseous malignant odontogenic tumor with prominent ghost cell keratinization and dentinoid formation. Here, we present the first case of GCOC arising in dentinogenic ghost cell tumor (DGCT), peripheral. The patient was a man in his 60s with an exophytic mass in the anterior part of lower gingiva. The resected tumor measured 4.5 cm in maximum diameter. Histologically, the nonencapsulated tumor proliferated in the gingiva without bone invasion. It was predominantly composed of ameloblastoma-like nests and islands of basaloid cells with ghost cells and dentinoid in the mature connective tissue, suggesting DGCT, peripheral. As minor components, sheets of atypical basaloid cells and ameloblastic carcinoma-like nests with pleomorphism and high proliferative activity (Ki-67 labeling index up to 40%) consistent with malignancy were identified. CTNNB1 mutation and β-catenin nuclear translocation were observed in both benign and malignant components. Final diagnosis was GCOC arising in DGCT, peripheral. GCOC shows similar histological features to DGCT. In this unique case without invasion, the cytological atypia and high proliferative activity supports the diagnosis of malignant transformation from DGCT.

Dentinogenic ghost cell tumor revisited from a single institution in China with focus on adenoid ameloblastoma-like features

OBJECTIVE

The present study aims to identify adenoid ameloblastoma (AdAM) from previously diagnosed cases of dentinogenic ghost cell tumor (DGCT), and gain insight to the possible relationship between AdAM and DGCT.

METHODS

DGCT cases diagnosed between 2006 and 2022 were re-examined with focus on the AdAM-like features.

RESULTS

A total of nine patients were included. Seven patients were males and two were females. The mean age was 38.0 ± 16.0 years. Five tumors occurred in the maxilla and four in the mandible, with a remarkable predilection for the posterior regions of both jaws. Microscopically, dentinoid material deposition was present in all cases. The ghost cells were absent in two cases. Rare ghost cells (<1%) were observed in three cases, and a higher proportion of ghost cells (5%-20%) were present in the remaining four cases. All cases showed prominent AdAM-like features, including duct-like structures, whorls/morules, and cribriform architecture. According to the diagnostic criteria proposed by the 2022 WHO classification, five cases without or with rare ghost cells were reclassified as AdAM. The other four cases including a higher proportion of ghost cells consisted of a mixture of DGCT and AdAM histopathologic patterns.

CONCLUSION

Our results confirmed that the AdAM-like features had been largely overlooked in the diagnosis of DGCT at our institution in the past. Whilst a subset can now be more accurately classified as AdAM, some tumors showed overlapping morphological features between AdAM and DGCT, suggesting that the two may represent a spectrum of the same entity.

A rare case of dentinogenic ghost cell tumor with concomitant odontoma

Key Clinical Message

A case of dentinogenic ghost cell tumor occurring simultaneously with a clinically diagnosed odontoma. The occurrence of epithelial and mesenchymal tumors at the same site is very rare, but should be kept in mind during pathological diagnosis.

Abstract

Dentinogenic ghost cell tumor (DGCT) is a rare and benign odontogenic tumor composed of ghost cells, calcified tissue, and dentin. We present an extremely rare case of a 32-year-old female who was clinically diagnosed with an odontoma presenting with a painless swelling in her maxilla. Radiographic examination showed a well-defined radiolucent lesion with tooth-like calcified areas. The tumor was resected under general anesthesia. No recurrence was noted at the 12-month follow-up. Histopathological examination of the surgically resected tumor yielded a diagnosis of DGCT with odontoma.