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Dentinogenic ghost cell tumor: Tumor in the garb of a cyst!

peripheral DGCT on histopathological examination of the excisional biopsy. The dentinogenic ghost cell tumor (DGCT) is a relatively uncommon locally invasive neoplasm that mimics several inflammatory/reactive lesions of the gingiva or odontogenic cysts. The confirmatory diagnosis of this rare lesion can only be made with histopathological examination. Routine staining reveals features of a “mixed” tumor as ghost cells with calcification, dysplastic dentin and islands of epithelium in rosette pattern in mature connective tissue are visible. The case report describes an asymptomatic growth in the maxillary gingiva of a young patient that was incidentally diagnosed as a DGCT after biopsy. Malignant transformation of this lesion to its more aggressive counterpart, odontogenic ghost cell carcinoma has been described, and hence, regular follow‑up of diagnosed cases is imperative. The purpose of the paper is to report a case that adds to the literature and this will consequently help to diagnose and understand the biological behavior of these lesions better. Abstract


INTRODUCTION
The calcifying odontogenic cyst (COC) was first described by Gorlin et al. in 1962. [1] Formerly, the solid variant of COC was called calcifying ghost cell odontogenic tumor. Primarily, it has the features of a cyst, but since it also has several prominent characteristics of a solid neoplasm, it was renamed dentinogenic ghost cell tumor (DGCT) by Praetorius et al. [2] Subsequently, the nomenclature of this tumor was changed to DGCT at the 2005 World Health Organization (WHO) histologic classification of odontogenic tumors. [3] DGCTs were considered to be the solid, neoplastic tumor counterpart of COCs, an extremely rare odontogenic tumor. COCs account for 1%-2% of all odontogenic tumors and 2%-14% of all COCs are solid tumors. [4] DGCT may occur intraosseously or less commonly as an extraosseously variant. Most extraosseous DGCTs are peripheral lesions arising in the gingival or alveolar mucosa. Their behavior is typically unaggressive and can be controlled by local excision. No recurrences have been reported. Intraosseous DGCTs are more aggressive than extraosseous DGCTs. More aggressive local resection is recommended for intraosseous DGCT, particularly if the tumor is radiologically ill-defined. [5] The case report describes a relatively painless, slow-growing asymptomatic lesion in the maxillary anterior gingiva that mimicked a reactive gingival lesion or a globulomaxillary cyst but turned out to be the extremely rare entity of a peripheral DGCT on histopathological examination of the excisional biopsy.
A 26-year-old male reported to the clinic of the oral and maxillofacial consultant with the chief complaint of a growth in the upper left front part of the jaw. The patient did not have any pain, but the swelling was causing discomfort to the patient. The patient revealed that the swelling was slow growing and had attained the current size gradually over the past 12-14 months [ Figure 1].
On extraoral examination, the base of the left ala was slightly raised. There was, however, no change in color/texture or erythema over the overlying skin or upper lip.
Intraorally, an ovoid mass was visible on the attached gingival between the maxillary left lateral incisor and canine. It had a reddish-pink color similar to the normal surrounding gingiva.
On palpation, it was firm and had a "ping-pong ball" feel. Written consent was obtained from the patient and the lesion was excised under local anesthesia [ Figure 2] and sent for histopathological examination. It was a well-encapsulated lesion [ Figure 3].
Histologically, under routine H and E staining, a connective tissue capsule with dentinoid tissue was distinctly visible. The cyst lumen showed characteristic ghost cells with calcification which are the hallmark of the dentinogenic ghost cell lesion [ Figures 4-6]. Some fields depicted sheets and rounded islands of odontogenic epithelium in mature connective tissue resembling rosettes. Polygonal and polyhedral cells showing hyperchromatic nuclei were also visible. Mitotic figures were not found in these tumor cells, and there was no evidence of malignant transformation in these patients, but the tumor invaded the surrounding cortical bone and soft tissue.

DISCUSSION
DGCT is an uncommon locally invasive neoplasm, representing approximately 1.9%-2.1% of the overall odontogenic tumors. [6] Peripheral DGCT is a rare odontogenic tumor, representing 13%-21% of all DGCTs. Clinically, it appears as a nodule of the gingival or alveolar mucosa and is usually asymptomatic. Peripheral occurrence of the cystic types of COCs is well documented in the English literature. [7] This may result from cortical bone perforation by a central lesion or more rarely, true peripheral origin from gingival epithelial remnants. [8] Candido et al., in their review of the literature, concluded that peripheral DGCTs mostly affect the canine region or the anterior part of the jaw. The patient age ranged from 41 to 83 years with an average age of 62. [9] Contrary to other odontogenic tumors, DGCT predominantly occurs in later life. [10] No predominance exists for the maxilla or mandible. [3] Histologically, DGCT is an infiltrative solid neoplasm composed of odontogenic epithelium associated with   Dentinoid is hyalinized eosinophilic material suggestive of immature or dysplastic dentin and is located closely near the epithelial sheet. [4] Sheets and rounded islands of odontogenic epithelium are seen in mature connective tissue. The epithelium of the tumor islands resembles that of an ameloblastoma. Minor cysts may form in the epithelial islands. A characteristic feature is the transformation of the epithelial cells into ghost cells. Individual as well as large islands of ghost cells may be seen. Some ghost cells undergo calcification and lose their cellular outline. [11] Ghost cells are swollen ellipsoidal keratinized epithelial cells that have lost their nuclei, leaving only a faint outline of the original nuclei. [12] Ghost cells are essentially requisite for the diagnoses of DGCT and COC. [13] Large islands or individual eosinophilic ghost cells are found in the epithelium as well as in the connective tissue.
The aggressive or malignant counterpart of DGCT, odontogenic ghost cell carcinoma (OGCC), combines architectural and cytologic malignant features with prominent mitotic activity, infiltrative growth pattern, locally aggressive, destructive behavior and occasional distant metastasis. [14] The malignant transformation of DGCT into OGCC has been described, [15] so patients with DGCT, especially recurrent DGCT, should remain in long-term follow-up.
Other differential diagnoses include inflammatory and reactive gingival lesions such as epulis, globulomaxillary cysts and the peripheral variant of the ameloblastoma.
DGCT can be distinguished from ameloblastoma by the presence of large numbers of ghost cells and dysplastic dentin. [16] Some results suggest that conservative curettage and enucleation were not appropriate for treating DGCT, and the biological behavior of DGCT requires further study. [17] The etiology remains an enigma till date and a thorough understanding of the pathophysiology ever since it has been described by Gorlin has been controversial.

Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest
There are no conflicts of interest.