Salivary Glands - Clinical Tree

Salivary glands are divided into major (parotid, submandibular, and sublingual) and minor salivary glands. Major salivary glands are paired structures, and minor glands exist in a submucosal location throughout the upper aerodigestive tract starting from the nasal cavity and lips down to the esophagus and trachea. Embryologically, the salivary glands are tubuloacinar structures arising from invaginations of the somatoderm (ectodermal) and foregut (endodermal). The salivary gland network is composed of secretory elements that produce saliva upon stimulation by mastication or sensory/autonomous nervous system stimuli (i.e., smell, taste, and thought).

The composition of saliva depends on the site of the salivary gland producing it. For example, a larger concentration of serous glands is found in the parotid and mucous glands in the hard palate. Saliva produced by these glands facilitates digestion, provides lubrication and protection of mucous membrane and dentition, and provides clearance of foreign materials. In addition, saliva contains enzymes (e.g., amylases, lipases, other enzymes) that initiate the digestive process, primarily of materials that contain starch. Saliva also plays an essential role in preventing dental caries and infection by direct cleansing of foreign materials and antibacterial activity that is mediated through multiple factors (i.e., immunoglobulin A and leukotrienes).

Neoplasms of the salivary glands are rare and account for approximately 3% to 6% of all tumors of the head and neck region. Cancers of the salivary gland occur with an incidence of approximately 2.5 to 3.0 cases per 100,000 per year in the United States. Factors that predispose to neoplastic processes in the major salivary glands include a history of exposure to low-dose radiation. In addition, chronic exposure to wood dust (especially soft wood) and chemicals used in the leather tanning industry also may increase the risk for minor salivary gland cancers in the sinonasal tract (especially adenocarcinomas). An increased incidence of adenocarcinoma of minor salivary origin of the nasal cavity and ethmoid region is reported from Europe, in contrast to the United States, where squamous cell carcinoma is most common in these sites. Although no known links exist, a higher rate of malignant oncocytomas in Alaskan natives suggests that other unidentified environmental and/or inherited factors also may contribute to salivary carcinogenesis.

The risk for malignancy and the histopathologic distribution of malignant tumors differs between major and minor salivary glands. The incidence of malignancy in the parotid, submandibular, and minor salivary glands is 25%, 50%, and 80%, respectively ( Fig. 13.1 ). Overall, 65% of salivary gland cancers arise in the parotid gland, 8% arise in the submandibular gland, and 27% arise in the minor salivary glands ( Fig. 13.2 ). The mucosa of the hard palate is the most frequent site of origin of minor salivary gland tumors, followed by other sites in the oral cavity and paranasal sinuses ( Fig. 13.3 ). The histologic classification of salivary tumors is shown in Table 13.1 .

Table 13.1

The World Health Organization Histologic Classification of Salivary Gland Tumors

Nonneoplastic epithelial lesions	Sclerosing polycystic adenosis Nodular oncocytic hyperplasia Lymphoepithelial sialadenitis Intercalated duct hyperplasia
Benign tumors	Pleomorphic adenoma Myoepithelioma Basal cell adenoma Warthin's tumor Oncocytoma Lymphadenoma Cystadenoma Sialadenoma papilliferum Ductal papillomas Sebaceous adenoma Canalicular adenoma and other ductal adenomas
Uncertain malignant potential	Sialoblastoma
Malignant tumors	Acinic cell carcinoma Secretory carcinoma Mucoepidermoid carcinoma Adenoid cystic carcinoma Polymorphous adenocarcinoma Epithelial myoepithelial carcinoma Clear cell carcinoma Basal cell adenocarcinoma Sebaceous adenocarcinoma Intraductal carcinoma Cystadenocarcinoma Adenocarcinoma not otherwise specified (NOS) Salivary duct carcinoma Myoepithelial carcinoma Carcinoma ex pleomorphic adenoma Carcinosarcoma Poorly differentiated carcinoma (undifferentiated carcinoma, large cell neuroendocrine carcinoma, and small cell carcinoma) Lymphoepithelial carcinoma Squamous cell carcinoma Oncocytic carcinoma

The most common benign tumor of salivary gland origin is the pleomorphic adenoma (mixed tumor). The parotid gland is the most common site of origin, followed by the submandibular gland and then by minor salivary glands. These tumors most frequently arise in the fifth to sixth decades of life and have a slight predilection for women. In general, pleomorphic adenomas tend to be asymptomatic and grow slowly; rapid growth raises concern for malignant transformation. Warthin's tumor is the next most common benign salivary neoplasm, which occurs most frequently in the tail of the parotid gland. An association with tobacco use has been suggested, because smokers have a fivefold to tenfold increased risk for these tumors. These tumors have a predilection for older white men and can be bilateral in up to 10% of cases.

Oncocytomas typically occur in older persons and are relatively rare. These tumors are characterized by a high mitochondrial content, which accounts for fluorodeoxyglucose avidity on positron emission tomography scans, similar to Warthin's tumors. Lymphoepithelial lesions are relatively rare but can occur in increased frequency in patients with human immunodeficiency virus infection, in whom they are often bilateral. Monomorphic adenoma is a term that was used in the past to describe a less heterogeneous group of tumors than pleomorphic adenoma that includes basal cell adenoma, canalicular adenoma, and myoepithelioma. Of these, basal cell adenoma is the most common and typically occurs in the parotid gland of older persons. Although canalicular adenomas also occur in older persons, they typically originate from the minor salivary gland of the upper lip and buccal mucosa.

The distribution of various types of malignant tumors of the salivary glands is shown in Fig. 13.4 . Mucoepidermoid carcinomas are found most commonly in the parotid gland, whereas adenoid cystic carcinomas are seen most frequently in submandibular and minor salivary glands. Histologic differentiation is crucial in predicting the biological behavior of salivary neoplasms. Low-grade malignant tumors have an indolent course and have an excellent prognosis. On the other hand, high-grade tumors behave aggressively, with increased risk of regional and distant metastasis, and are associated with poor prognosis.

Mucoepidermoid carcinoma is the most common malignant salivary gland tumor. Based on their histologic features, these tumors are further subdivided into low-grade, intermediate-grade, and high-grade tumors. Although low-grade and intermediate-grade tumors are slow growing, they can be locally aggressive; however, they rarely metastasize. In contrast, high-grade mucoepidermoid carcinomas have an aggressive clinical course with local invasion and increased risk of regional nodal metastasis.

Mucoepidermoid carcinomas can arise not only in minor salivary glands but also in salivary nests within the mandible (i.e., a “central salivary carcinoma”) and in ectopic salivary tissue in the parapharyngeal space.

Adenoid cystic carcinoma is the most common malignant tumor of the submandibular and minor salivary glands. Although grading systems have been proposed for these tumors, tumor grading does not seem to influence the behavior of adenoid cystic carcinomas. These tumors have a high degree of neurotropism, leading to the propensity for perineural spread. Although the overall outcome of adenoid cystic carcinomas is poor, the disease course typically is protracted, with survival measuring in decades, even in the presence of distant metastases . Although regional lymph node metastases are uncommon, pulmonary metastases occur frequently.

Polymorphous adenocarcinomas occur mainly in minor salivary glands and typically have an indolent course. These tumors most commonly arise in the oral cavity, with the hard palate being the principal site of origin. The “adenocarcinoma not otherwise specified (NOS)” category includes a heterogenous group of neoplasms that lacks any of the histologic features that characterize the other defined types of salivary tumors. Among other malignant tumors are acinic cell carcinomas, mammary analog secretory carcinoma, salivary duct carcinoma, myoepithelial carcinoma, and carcinoma ex pleomorphic adenoma. About 10% of malignant neoplasms of salivary origin are acinic cell carcinomas, and they most commonly arise from the parotid gland. These tumors tend to be indolent but have the capacity of high-grade tumors.

Primary squamous cell carcinoma of the parotid gland is extremely rare and needs to be differentiated from squamous cell carcinoma that has metastasized to an intraparotid lymph node from a synchronous or previously treated skin cancer.

Evaluation

Tumors of salivary gland origin usually present as an asymptomatic mass. The majority of parotid tumors arise in the superficial lobe and present as a rubbery nodular mass, generally located anterior to the lobule of the ear in the region of the tail of the parotid gland ( Figs. 13.5 through 13.7 ). Most mixed tumors are asymptomatic. Facial paralysis does not occur with mixed tumors regardless of the size of the tumor. Enlarged ipsilateral cervical lymph nodes or the presence of facial nerve dysfunction or invasion of the overlying skin almost invariably are suggestive of a malignant tumor ( Figs. 13.8 through 13.11 ). Tumors in the deep lobe of the parotid gland usually present with diffuse enlargement and fullness in the retromandibular region.

Figure 13.5, A large benign mixed tumor of the right parotid gland. Note stretched skin over the tumor.

Figure 13.6, The anterior view of a patient with a benign mixed tumor of the left parotid gland.

Figure 13.7, A large parotid tumor of the left parotid gland.

Figure 13.8, Involvement of a periparotid or cervical lymph node by metastasis is almost diagnostic of a malignant parotid tumor.

Figure 13.9, Invasion of the overlying skin is highly suggestive of a malignant tumor.

Figure 13.10, The lateral view of a patient with a carcinoma of the parotid gland.

Figure 13.11, Facial nerve paralysis is diagnostic of a malignant tumor of the parotid gland.

Radiographic studies are essential to accurately delineate the location and extent of the deep lobe tumor. Tumors of the deep lobe of the parotid gland, extending into the parapharyngeal space, may cause medial displacement of the soft palate, tonsil, and/or lateral pharyngeal wall ( Fig. 13.12 ). They may or may not be associated with a palpable parotid mass. Occasionally tumors may arise in accessory parotid tissue along the course of the Stensen duct and present as a mass in the soft tissues of the midportion of the cheek ( Fig. 13.13 ). Metastatic tumors to the parotid gland from primary cutaneous malignant lesions of the scalp and forehead such as squamous cell carcinomas and melanomas also are important differential diagnostic entities. Diffuse enlargement of the entire parotid gland may be seen in patients with lymphoma, Sjogren's syndrome, and those with extensive eosinophilic infiltrate, as seen in patients with Kim-Kimura's disease ( Fig. 13.14 ).

Figure 13.12, A deep lobe parotid tumor presenting as a parapharyngeal mass.

Figure 13.13, An accessory parotid tumor.

Figure 13.14, Diffuse enlargement of the entire parotid gland with a firm to hard mass (Kim-Kimura disease).

A painless swelling in the submandibular triangle is the usual presenting symptom for a tumor of the submandibular gland ( Fig. 13.15 ). The presence of pain signifies an obstructive and/or inflammatory phenomenon and may prove to be sialadenitis of the submandibular salivary gland. Bimanual palpation of the mass through the floor of the mouth confirms the location of the tumor in the submandibular gland and differentiates this entity from adjacent enlarged cervical lymph nodes.

Figure 13.15, A mixed tumor of the submandibular salivary gland.

Tumors of minor salivary gland origin usually present as a submucosal mass that may be ulcerated ( Figs. 13.16 and 13.17 ). The majority of tumors of minor salivary gland origin are malignant. Minor salivary tumors of the lip often mimic a mucocele or a mucous cyst ( Fig. 13.18 ). The presence of a soft-to-firm rubbery submucosal mass should raise the index of suspicion regarding the possibility of a minor salivary gland tumor.

Figure 13.16, An adenoid cystic carcinoma of the hard palate.

Figure 13.17, A malignant mixed tumor of the hard palate.

Figure 13.18, An adenocarcinoma of the upper lip.

Radiographic Evaluation

Diagnostic imaging studies are necessary if clinical examination does not provide accurate delineation of the location and extent of the tumor. Thus imaging is essential in the evaluation of a deep-seated or a fixed lesion for which invasion into adjacent anatomic structures is a concern. Plain radiographs, sialography, nuclear scans, and ultrasonography add very little to the desired diagnostic information and are seldom indicated. On the other hand, computerized tomography (CT) and magnetic resonance imaging (MRI) permit better visualization of masses of the salivary glands.

CT and MRI are equally satisfactory in differentiating cystic from solid lesions and allow evaluation of the relationship of the mass to the major salivary gland or adjacent structures, including soft tissues and bones ( Figs. 13.19 through 13.21 ). For minor salivary lesions, CT provides valuable information that assists in treatment planning; in particular, it shows the relationship of the tumor to surrounding structures and demonstrates tumor extension, permitting assessment of the resectability of advanced lesions. CT scans are invaluable in the evaluation of deep lobe parotid tumors and assist in differentiating them from tumors arising in the parapharyngeal space ( Figs. 13.22 through 13.25 ). MRI is equally valuable in the assessment of deep lobe parotid tumors and in differentiating them from tumors of ectopic or minor salivary gland origin ( Fig. 13.26 ). CT scans are particularly of value in the assessment of bone erosion, whereas MRI is of particular value in demonstrating tumor extension along cranial nerves.

Figure 13.19, A computed tomography scan showing bilateral Warthin's tumors, which are multiloculated on the right-hand side ( arrow ) and uniloculated on the left-hand side.

Figure 13.20, A T1-weighted magnetic resonance imaging scan showing a benign mixed tumor in the superficial lobe of the left parotid gland ( arrow ).

Figure 13.21, A T2-weighted magnetic resonance imaging scan showing a benign mixed tumor in the superficial lobe of the left parotid gland ( arrow ).

Figure 13.22, An axial view of a computed tomography scan showing a deep lobe parotid tumor ( arrow ).

Figure 13.23, A coronal view of the computed tomography scan of the same patient as in Fig. 13.20 showing the deep lobe parotid tumor ( arrow ).

Figure 13.24, An axial view of a magnetic resonance imaging scan of the same patient as in Fig. 13.20 showing the deep lobe parotid tumor ( arrow ).

Figure 13.25, A coronal view of the magnetic resonance imaging scan of the same patient as in Fig. 13.20 showing the deep lobe parotid tumor ( arrow ).

Figure 13.26, An axial view of a contrast-enhanced T2-weighted magnetic resonance imaging scan showing a left parapharyngeal space tumor of ectopic salivary tissue. Note fat separating the tumor from adjacent deep lobe parotid tissue.

Pathology

Histologically, major and minor salivary glands consist of the secretory acinus and related ducts and myoepithelial cells. Acini may be serous, mucous, or mixed serous and mucinous. The cytoplasm of serous cells contains zymogen granules, and their principle secretion is amylase. The cytoplasm of mucinous cells is clear and contains mucin. Secretions from the acini empty into smaller duct systems that lead to branching larger duct systems and eventually into the main excretory duct ( Fig. 13.27 ). Myoepithelial cells surround the acinar and ductal cells.

Figure 13.27, The histologic structure of the normal salivary gland.

In most patients presenting with the clinical features of a discrete parotid tumor, tissue diagnosis is seldom required before surgical exploration. However, if clinical suspicion of a malignant tumor is high, then cytologic diagnosis of a malignant tumor can be established by a fine-needle aspiration biopsy. Aspiration with a 21-gauge needle is usually satisfactory in securing tissue for diagnosis or as a screening tool to triage the patients to different treatment. The rate of correctly establishing the diagnosis as benign or malignant range from 81% to 98%; however, a specific diagnosis can be made in only 60% to 75%. Inadequate sampling appears to be the most frequent cause of false negatives.

Pleomorphic Adenoma (Mixed Tumor)

Pleomorphic adenoma is a benign neoplasm characterized by an admixture of epithelial, myoepithelial, and stromal elements with architectural pleomorphism. This neoplasm represents two-thirds of all tumors of the major salivary glands and less than half of those in the minor salivary glands, with the greatest frequency of occurrence in the superficial lobe of the parotid gland.

Grossly, pleomorphic adenoma is generally white and firm, with a smooth outer and cut surface. The tumor may be vaguely lobulated and nodular, with “podocytes,” which are more commonly noted microscopically. Microscopically, pleomorphic adenomas demonstrate an admixture of epithelial and mesenchymal elements, with ductal and myoepithelial cell types intermingled with myxoid, mucoid, or chondroid stroma ( Figs. 13.28 and 13.29 ). Most pleomorphic adenomas are encapsulated, especially in the major salivary gland, with a variable amount of capsule thickness. Irregular peripheral borders and local extension of fingerlike processes into the capsule might be seen. Pleomorphic adenomas are characterized by a remarkable degree of morphologic diversity between individual tumors or within a single tumor. Therefore a definite diagnosis might not be possible on a representative frozen section or on a small amount of fine-needle aspiration material. Recurrence of pleomorphic adenomas generally represents local regrowth and not necessarily malignancy, and further surgery becomes technically demanding with reference to the safety of the facial nerve. Many recurrent pleomorphic adenomas are multifocal, and some can be so widely distributed that surgical control becomes impossible.

Figure 13.28, Pleomorphic adenoma demonstrating abundant myxochondroid matrix and myoepithelial cells (25× H&E stain).

Figure 13.29, Pleomorphic adenoma demonstrating abundant myxochondroid matrix and myoepithelial cells (50× H&E stain).

Carcinoma ex pleomorphic adenoma is a malignant neoplasm that arises in association with pleomorphic adenoma. Typically, these tumors are high grade and show similar histology to their de novo counterparts. The malignant tumor component is most frequently salivary duct carcinoma, followed by myoepithelial carcinoma. However, any histologic subtype of salivary gland carcinoma can arise in association with pleomorphic adenoma. Carcinoma ex pleomorphic adenoma is classified based on the degree of tumor invasion through the preexistent pleomorphic adenoma capsule into the surrounding tissue as intracapsular, minimally invasive, and invasive. The extent of invasion has been found to correlate with the clinical outcome. A very low rate of local recurrence and regional metastases are noted in patients with intracapsular minimally invasive tumors, while the risk of local recurrence, metastases, and fatal outcome is higher in patients with invasive tumors. At the molecular level, rearrangements of PLAG1 (pleomorphic adenoma gene 1) on 8q12 and HMGA2 on 12q14-15 are the most frequent genetic alterations in both pleomorphic adenoma and carcinoma ex pleomorphic adenoma.

Warthin's Tumor (Papillary Cystadenoma Lymphomatosum)

Warthin's tumors are benign salivary gland neoplasia that usually arise in the parotid gland and are composed of eosinophilic glandular epithelium, lined by basaloid cells, with papillary cystic spaces, embedded in dense lymphoid tissue ( Fig. 13.30 ).

Figure 13.30, Warthin's tumor with adjacent normal parotid gland parenchyma on the right (50× H&E stain).

Oncocytoma

Oncocytoma, also known as oxyphil adenoma or oncocytic adenoma, is a benign salivary gland neoplasm composed of oncocytes that are benign epithelial cells packed with mitochondria, imparting a granular appearance to the cytoplasm ( Fig. 13.31 ).

Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma is the most common malignant salivary gland tumor in both adults and children. More than half of these tumors occur in the parotid gland; when they arise in the minor salivary glands, they are most frequently in the palate.

Histologically, this tumor is composed of varying proportions of epidermoid (squamoid), mucous, and intermediate cells, arranged in cystic or glandular structures or in a solid growth pattern. Mucicarmine stain highlights intracytoplasmic mucin. CK5/6 and p63 immunohistochemical stains will stain the epidermoid and intermediate cells. S100 and myoepithelial markers (Calponin and smooth muscle actin) are usually negative in mucoepidermoid carcinoma. Variable histologic parameters such as perineural invasion and vascular invasion have been reported to correlate with the patients’ clinical outcome. However, prognosis seems to be largely dependent on tumor grade. Several grading systems exist for mucoepidermoid carcinomas, but they are graded by most pathologists, using three tiers (based on tumor cytologic and proliferative features and architecture): low, intermediate, and high grade ( Fig. 13.32 and Fig. 13.33 ). At the molecular level, a chromosomal translocation (11,19), resulting in MECT1/MAML2 fusion genes, has been identified in 40% to 80% of mucoepidermoid carcinomas. The translocation has been suggested to be associated with more indolent clinical behavior.

Figure 13.32, Low-grade mucoepidermoid carcinoma with more than 20% of the tumor represented by cystic spaces lined by squamoid epithelial cells (25× H&E stain).

Figure 13.33, High-grade mucoepidermoid carcinoma demonstrating marked nuclear pleomorphism and areas of single-cell necrosis (200× H&E stain).

Adenoid Cystic Carcinoma

Adenoid cystic carcinoma is a slowly growing, insidious salivary gland malignancy, occurring in both minor and major glands, notorious for its tendency for perineural invasion, as well as local invasion and recurrence after surgical resection. These tumors may arise in the major salivary glands and also in the oral cavity, nasopharynx, nasal cavity, paranasal sinuses, lacrimal glands, and lower respiratory tract. Adenoid cystic carcinoma grows as solid, white to gray, scirrhous, infiltrative masses that tend to be hard and fixed and may tether overlying skin.

Histologically, adenoid cystic carcinoma is composed of ductal and myoepithelial cells and shows hyalinized or myxoid matrix ( Fig. 13.34 ). The tumor demonstrates three main growth patterns: cribriform, tubular, and solid ( Fig. 13.35 ). Perineural invasion is commonly seen in adenoid cystic carcinoma ( Fig. 13.36 ).

Figure 13.34, Adenoid cystic carcinoma of the parotid gland demonstrating a predominantly cribriform architectural pattern (50× H&E stain).

Figure 13.35, Area of solid growth in adenoid cystic carcinoma, with rare ductal cells and a predominance of myoepithelial cells (400× H&E stain).

Figure 13.36, Perineural invasion is present centrally within this adenoid cystic carcinoma (400× H&E stain).

Unlike mucoepidermoid carcinoma, grading of adenoid cystic carcinoma does not seem to be significant in the prediction of the behavior of this malignancy. The presence of solid tumor growth seems to correlate with more aggressive behavior and poor survival. It is infrequent to see lymph node metastases; rather, one is more likely to see distant spread to the lungs and solid organs such as the kidney, with as much as a 15-year latency period.

The MYB protooncogene occurs in the majority of adenoid cystic carcinomas, with a translocation (6,9) resulting in fusion of the MYB and NFIB genes being the most common mechanism. The 6,9 translocation has been described in about 65% of adenoid cystic carcinomas of the head and neck and various anatomic sites, including the breast and lung.

Polymorphous Low-Grade Adenocarcinoma

Polymorphous low-grade adenocarcinoma (PLGA), now shortened to polymorphous adenocarcinoma (PAC), occurs mainly in minor salivary glands, with the hard palate being the most common location. It is important to differentiate PAC from adenoid cystic carcinoma since it typically has an indolent course. These tumors show one cell type with cytologic uniformity and various growth patterns. Perineural invasion may be seen. A cribriform variant, which is considered a separate entity by some authors, has been reported to have a greater capacity for regional metastasis. Activation of PRKD1 point mutation has been recently reported in about 73% of PLGA.

Epithelial-Myoepithelial Carcinoma

Epithelial-myoepithelial carcinoma is another typically indolent salivary gland tumor that is characterized by a multinodular pattern and biphasic or bilayered arrangement of inner ductal cells and outer myoepithelial cells, with classically clear cytoplasm.

Acinic Cell Carcinoma

Acinic cell carcinomas account for approximately 10% of all malignant salivary gland carcinomas and arise almost exclusively in the parotid. These tumors are characterized by serous acinar cell differentiation with zymogen-type cytoplasmic granules. They tend to be indolent and low grade but have the capacity to present as high-grade tumors.

Secretory Carcinoma

Mammary analog secretory carcinoma (MASC) is a recently described salivary gland tumor that was likely classified as acinic cell carcinoma in the past. The tumor has striking histologic and molecular similarities to secretory carcinoma of the breast. The official terminology of this entity is now “secretory carcinoma.” At the histologic level, tumor cells have eosinophilic or clear bubbly cytoplasm, and they may grow as tubules or microcysts, papillae, or macrocysts. Secretions are almost always present in the microcysts and/or macrocysts. MASC characteristically harbors a balanced chromosomal translocation (12, 15), resulting in the formation of the ETV6–NTRK3 fusion genes.

Salivary Duct Carcinoma

Salivary duct carcinoma is an aggressive, high-grade carcinoma that resembles high-grade breast ductal carcinoma. Typically the tumor is composed of ductal cells arranging in tubules, as solid and cribriform growth with central necrosis ( Fig. 13.37 ). Androgen receptor (AR) expression by immunohistochemistry is identified in the vast majority of salivary duct carcinoma. In addition to AR, immunohistochemical overexpression of human epidermal growth factor receptor 2 (HER2) has been reported in a good percentage of salivary duct carcinoma with or without amplification of the gene by fluorescence in situ hybridization. Targeted therapeutic modalities, including anti-ERBB2 antibodies and androgen deprivation therapy, are characterized by variable results. Additionally, various genetic alterations have been reported in salivary duct carcinoma, including TP53, PTEN, EGFR, and phosphoinositide 3-kinase (PIK3CA) pathway.

Myoepithelial Carcinoma

Myoepithelial carcinoma is a rare salivary gland tumor that is composed almost exclusively of myoepithelial cells. The tumor seems to be locally aggressive with diverse clinical outcome. Both myoepithelial carcinoma and salivary duct carcinoma may arise de novo or in association with pleomorphic adenoma (carcinoma ex pleomorphic adenoma).

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