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Myoepithelial carcinoma (MC) is an uncommon malignant neoplasm of the salivary glands composed predominantly of neoplastic myoepithelial cells. It may arise de novo or from malignant transformation of a pre-existing pleomorphic adenoma or benign myoepithelioma. Although some tumors exhibit low-grade features, myoepithelial carcinoma is generally considered potentially aggressive, with a risk of local recurrence and distant metastasis.
Definition and Classification
Myoepithelial carcinoma is defined by malignant proliferation of cells showing myoepithelial differentiation, without a significant ductal component. The World Health Organization recognizes MC as a distinct salivary gland carcinoma.
The tumor may show a variety of cellular morphologies, including:
- Spindle cells- Plasmacytoid (hyaline) cells
- Epithelioid cells
- Clear cells
This morphologic diversity contributes to diagnostic difficulty.
Epidemiology and Etiology
- Rare tumor, accounting for <1% of salivary gland malignancies
- Occurs across a wide age range, most commonly in adults
- No strong gender predilection
- Etiology is poorly understood
- May develop from long-standing pleomorphic adenoma or benign myoepithelioma
Common Sites of Occurrence
Myoepithelial carcinoma arises in both major and minor salivary glands:
- Parotid gland (most common)- Submandibular gland
- Minor salivary glands of the palate, buccal mucosa, and lips
Minor salivary gland lesions are often diagnosed late due to their indolent appearance.
Clinical Presentation
Clinical features are variable and may include:
- Slow- or rapidly growing salivary gland mass
- Firm or fixed swelling
- Pain or tenderness in advanced lesions
- Facial nerve dysfunction (parotid tumors)
- Ulceration in intraoral lesions
Clinical behavior is unpredictable and not always correlated with histologic appearance.
Diagnostic Approach
Accurate diagnosis requires integration of clinical findings, histopathology, and immunohistochemistry.
Key steps include:
- Imaging (CT or MRI) to assess local invasion
- Incisional biopsy for definitive diagnosis
- Histopathological examination
- Extensive immunohistochemical profiling
Immunohistochemistry
Tumor cells typically express:
- Myoepithelial markers: S100, calponin, smooth muscle actin (SMA), p63
- Cytokeratins
- Variable Ki-67 proliferation index (higher in aggressive tumors)
Loss of myoepithelial marker expression may indicate high-grade transformation.
Histopathological Features
Microscopic characteristics include:
- Infiltrative growth pattern
- Cellular pleomorphism and atypia
- Increased mitotic activity
- Necrosis in high-grade tumors
- Absence or minimal presence of ductal structures
- Possible perineural and lymphovascular invasion
The diagnosis of malignancy is based on invasive growth, cytologic atypia, and mitotic activity rather than architectural pattern alone.
Differential Diagnosis
Myoepithelial carcinoma must be differentiated from:
- Benign myoepithelioma- Pleomorphic adenoma
- Epithelial-myoepithelial carcinoma
- Clear cell carcinoma
- Sarcomatoid carcinoma
Immunohistochemistry is essential for accurate distinction.
Management and Treatment
Management depends on tumor grade and extent but is generally aggressive:
- Wide surgical excision with clear margins- Neck dissection in cases with nodal involvement
- Adjuvant radiotherapy for high-grade, invasive, or recurrent tumors
- Chemotherapy has limited effectiveness and is reserved for advanced disease
Long-term follow-up is essential due to the risk of late recurrence.
Prognosis
- Prognosis is variable and depends on tumor grade and stage
- Local recurrence rates range from 30–50%
- Distant metastasis (lung, bone) may occur, especially in high-grade tumors
- Overall survival is poorer than for low-grade salivary gland carcinomas
Role of Dental and Medical Professionals
Dental professionals play a crucial role in:
- Early detection of suspicious salivary gland lesions
- Monitoring long-standing benign tumors for malignant change
- Prompt referral for biopsy and specialist care
- Post-treatment oral rehabilitation and surveillance
For students, myoepithelial carcinoma highlights the importance of recognizing cell lineage differentiation and understanding the role of immunohistochemistry in salivary gland pathology.
Conclusion
Myoepithelial carcinoma is a rare but clinically significant salivary gland malignancy with unpredictable behavior. Accurate diagnosis relies on careful histopathologic assessment supported by immunohistochemical confirmation of myoepithelial differentiation. Early surgical management and diligent long-term follow-up are essential to optimize patient outcomes.