Adenoid cystic carcinoma of the palate: case report and review of literature

Adenoid Cystic Carcinoma (ACC) is a rare tumor constitutes for less than 1% of head and neck malignancies and 10% of all salivary gland tumors. Palate is the most common site to be involved in the oral cavity followed by parotid gland and submandibular gland. They are usually asymptomatic, slow growing, characteristically shows infiltrative growth and perineural invasion. This paper reports a case of Adenoid Cystic Carcinoma in a 35 year old female man reported with a swelling on the left side of palate involving the hard and soft palate since 8 months which was diagnosed histopathologically and review of literature of the peculiar clinical, and histopathological features.


Introduction
Adenoid cystic carcinoma is a malignant neoplasm that may affect either the major or minor salivary glands of the oral cavity [1,2]. It was first described by three Frenchmen (Robin, Lorain, and Laboulbene) in two articles published in 1853 and 1854. It was they who described the cylindrical appearance of this tumor. Billroth, in1859, first described ACC under the name "cylindroma", for its cribriform appearance formed by tumor cells with cylindrical pseudolumina or pseudospaces and described that ACC had a "great tendency to recur [3]." It accounts for about 5% to 10% of all salivary gland neoplasms, representing 2% to 4% of malignant occurrences of the head and neck area. Approximately 31% of lesions affect minor salivary glands, particularly the palate, though they can also be observed in the submandibular and parotid glands [4]. Although it presents a widespread age distribution, peak incidence occurs predominantly among women, between the 5 th and 6th decades of life [5]. Typical clinical findings include slow growth, local recurrence, perineural invasion and distant metastasis [6].
Three histological subtypes of ACC are known: cribriform, tubular and solid. They may occur either separately or together in the same tumor, and the solid subtype is the most aggressive [7]. A unique feature of ACC is the propensity for perineural invasion, even with early-stage tumors. Tumor is graded according to Szanto et al. [8] cribriform or tubular (grade I), less than 30% solid (grade II), or greater than 30% solid (grade III). It is currently recognized that ACC remains an extremely difficult disease to treat. It was described by Conley and Dingman as "one of the most biologically destructive and unpredictable tumors of the head and neck [9]". We report a case of adenoid cystic carcinoma of palate and a brief literature review on its clinical, histopathological and therapeutic aspects.

Discussion
The adenoid cystic carcinoma constitutes approximately 29.6% of minor salivary gland tumors. Often palate is the most commonly involved site, tongue being the second most common; other sites are floor of mouth, and lip [10]. ACC occurs most often in minor salivary glands and the submandibular gland, and less frequently in the sublingual and parotid glands. Other rare locations include the aerodigestive tract, minor salivary glands, lachrymal glands and adnexal skin glands [7]. Rarely, it may also present as primary intraosseous tumors of the maxilla and mandible. ACC is thought to arise from the mucous-secreting glands. It arises specifically from the intercalated ducts, and electron microscopy shows that it arises from cells that can differentiate into epithelial and myoepithelial cells. These mucus-secreting tumors are confined to structures derived from the foregut (that is, the parotid, submandibular, and sublingual glands, and the mucus glands throughout the upper respiratory tract) [7]. Most frequent clinical feature of adenoid cystic carcinoma affecting major salivary gland is reported to be the presence of tumor-usually 2-4 cm at its greatest diameter and intraoral adenoid cystic carcinoma seldom larger than 3 cm at its greatest diameter [11,12]. The lesion is uncapsulated and infiltrative; invasion of underlying bone is common.

Conclusion
Salivary gland tumors should be considered in the differential diagnosis of aggressive lesions in maxilla and mandible and especially when the aggressive lesion is involving palate, adenoid cystic carcinoma involving minor salivary gland tumors should be considered in differential diagnosis. The primary treatment objective in adenoid cystic carcinoma patients is local control, normal functionality and distant metastasis prevention. For this purpose, early detection of the lesion is a requirement, in order to enable a more favorable prognosis and better quality of life.

Competing interests
The authors declare no competing interest.

Authors' contributions
All authors have read and agreed to the final version of this manuscript and have equally contributed to its content and to the management of the case.