Salivary Gland Malignancies

Malignant Salivary gland neoplasms

The most common site for salivary gland tumors is the parotid gland, accounting for 61% to 80% of all cases. Fortunately, a relatively low percentage of parotid tumors are malignant, ranging from 15% to 32%, with the mucoepidermoid carcinoma appearing to be the most frequent overall. The frequency of malignancy in Sub-mandibular gland is much greater than that of the parotid gland, Adenoid cystic carcinoma is the most common malignancy, ranging from 11% to 17% of all cases. However, 70% to 95% of sublingual tumors are malignant. It can be stated that the smaller the gland is, the greater is the likelihood of malignancy for a salivary gland tumor.

Mucoepidermoid carcinoma is the most frequent malignancy of minor gland origin, comprising 13% to 23% of all tumors. Adenoid cystic carcinoma and polymorphous low-grade adenocarcinoma are also recognized as relatively common malignant tumors arising from the minor salivary glands. The most frequent site for minor salivary gland tumors are Palate > Upper lip > buccal mucosa. Although mucoceles are commonly found on the lower lip, this is a surprisingly rare site for salivary gland tumors (mostly mucoepidermoid carcinomas). Up to 95% of retromolar tumors are malignant, also because of a predominance of mucoepidermoid carcinomas. Unfortunately, most tumors in the floor of the mouth and tongue are also malignant. Important and most common tumours are discussed in brief:

1.      Mucoepidermoid carcinoma:

 It  is the most common salivary gland malignancy in children and young adults,with a peak incidence in he second decade of Iife. The parotid is the most common site for MEC, followed by the palate, submandibular gland, and other intraoral minor salivary gland sites . Primary intraosseous (central) MECs are rare.

Clinical features

The clinical resentation varies depending on tumour si e, size, and grade. Cystic intraoraI MEC can mimic a mucocoele. Mucinous MEC may fluctuate in size due to cyst rupture and may present as a mucin- draining cutaneous is fistula.

Histopathology

MEC is characterized by variable components of squamoid, mucin-producing, and intermediate type cells. , with a cystic and solid growth pattem. Oncocytic, clear-cell, and Sclerosing  variants have been described. The rare oncocytic variant is composed mainly of polygonal/columnar oncocytic cells with scattered mucocytes, and few if any squamoid cells . The sclerosing variant is characterized by dense hyalinizing fibrosis . Solid MECs tend to demonstrate predominant squamoid and intermediate cells, with a subtle transition between these two components.

Low-grade MEC is cystic, mucous cell rich, and well circumscribed. Intermediae-grade MECs are generally more solid and less circumscribed and show a diversity of appearances, including mucin extravasation. High-grade MEC displays one or more of the following features: nuclear anaplasia; necrosis; increased mitotic rate; and perineural, lymphovascular, or bony invasion.

Prognosis and predictive factors

Low- and intermediate-grade MECs are less aggressive and are generally curedcby complete surgical excision  The 10 -year overall survival rates for low-, intermediate-, and high –grade M ECs are approximately 90% , 70% , and 25% , respectively.

2.      Adenoid cystic carcinoma:

Adenoid cystic carcinoma (ACC) is a slow-growing and relentless salivary gland malignancy composed of epithelial and myoepithelial neoplastic cells that form various patterns, including tubular, cribriform. and solid forms. The median patient age at diagnosis is 57 years. There is no ethnic predilection, and the female-to-male ratio is about 1 . 5. ACC occurs most frequently in the major salivary glands, but more than one third of cases occur in minor glands in the oral cavity, sinonasal tract, or (rarely) other sites.

Clinical features

Patients usually present with swelling or masses, and may have numbness, paraesthesia, or pain. Involvement of motor nerves can cause facial or tongue weakness. ACC typically presents as a firm, g reyish- white, unencapsulated and infiltrative mass of variable size.

Histopathology

ACCs can manifest a variety of tubular and cribriform structures with variably solid components. The most recognizable architectural form is the cribriform pattern, characterized by nests of tumour cells interrupted by sharply punched-out spaces filled with basophilic matrix. The tubular pattern is composed of bilayered tubules with true lumina. The tumour cells show scant cytoplasm and typically have small angulated and hyperchromatic nuclei. The solid growth pattern is characterized by sheets of tumour cells without lumen formation and may consist of epithelial or myoepithelial elements.

Prognosis and predictive factors

Radical surgical excision, with or without postoperative radiation, is the treatment of choice. The 10-year survival rate is 50-70% and the local recurrence rate is highly variable. Lymph node involvement is uncommon, but is more frequent in solid variant . Distant metastasis is reported in > 50% of cases, most commonly to the lungs, followed by bone, liver, and brain.

3.      Acinic cell carcinoma:

Acinic cell carcinoma is a malignant salivary gland neoplasm composed of cancer cells with acinar features. The mean patient age at presentation is approximately 50 years, with a female-tamale ratio of  1 . 5 : 1. Acinic cell carcinoma is the second most common salivary gland malignancy in children. More than 90-95% of acinic cell carcinomas occur in the parotid glands.

Clinical features

The tumours typically present as slow growing, solitary, unfixed masses, but some are multinodular and/or fixed to skin. One third of patients experience pain and 5-1 0% develop facial paralysis.

Histopathology

Acinar and ductal cells with variable vacuolated, clear, oncocytic, and hobnail features forming solid, microcystic, and follicular patterns are present. The acinar cells are large and polygonal, with basophilic granular cytoplasm and round , eccentric nuclei. A subset of tumours may display an undifferentiated component, predominantly solid or cribriform with glandular patterns and areas of necrosis.

Prognosis and predictive factors

Although acinic cell carcinoma is generally not aggressive. a proportion can metastasize to cervical lymph nodes and lung. A recurrence rate as high as 35% has been reported. The 20-year survival rate is appromately 90%, with a slightly better rate for  females. Poor prognostic factors include large tumour size, involvement of the deep lobe of the parotid gland, and incomplete resection. Multiple recurrences and cervical lymp h node and distant metastases predict poor prognosis.