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Adenoid Cystic Carcinoma (ACC) is a malignant epithelial tumor of salivary gland origin, characterized by slow but relentless growth, a marked tendency for perineural invasion, and a high rate of late recurrence and distant metastasis. Although considered a low- to intermediate-grade malignancy histologically, ACC often demonstrates aggressive clinical behavior, making long-term follow-up essential.
Definition and Classification
Adenoid cystic carcinoma is defined as a malignant neoplasm composed of ductal and myoepithelial cells arranged in characteristic architectural patterns. The World Health Organization recognizes ACC as a distinct salivary gland carcinoma.
Three histopathologic growth patterns are described:
- Cribriform (most common and classic)- Tubular
- Solid (associated with poorer prognosis)
Most tumors show a combination of these patterns.
Epidemiology and Etiology
ACC accounts for a significant proportion of malignant salivary gland tumors and affects a wide age range, typically presenting in middle-aged adults. There is no strong gender predilection.
Risk factors are not well defined, though associations include:
- Minor salivary gland origin- Possible genetic alterations involving MYB and MYBL1 gene rearrangements
- Prior radiation exposure (less common)
Common Sites of Occurrence
ACC most frequently arises in:
- Minor salivary glands (especially the palate)- Parotid gland
- Submandibular gland
- Sublingual gland
Extraoral sites include the lacrimal glands, tracheobronchial tree, and breast.
Clinical Presentation
ACC often presents with subtle but characteristic features:
- Slow-growing, firm swelling- Pain or paresthesia due to perineural invasion (a hallmark feature)
- Ulceration in advanced intraoral lesions
- Facial nerve involvement in major salivary gland tumors
Pain out of proportion to lesion size should raise suspicion for ACC.
Diagnostic Approach
Diagnosis requires careful correlation of clinical, radiologic, and histopathologic findings.
Key steps include:
- Imaging (MRI preferred) to evaluate perineural spread- Fine-needle aspiration cytology (FNAC) for preliminary assessment
- Incisional biopsy for definitive diagnosis
- Histopathological evaluation and grading
Immunohistochemistry may show positivity for cytokeratins, S100, SOX10, and myoepithelial markers.
Histopathological Features
Characteristic microscopic features include:
- Cribriform pattern with pseudocystic spaces containing basophilic mucopolysaccharide material (“Swiss cheese” appearance)- Tubular structures lined by ductal and myoepithelial cells
- Solid sheets of basaloid cells in high-grade tumors
- Frequent perineural invasion
- Infiltrative growth pattern
The proportion of solid components correlates with worse prognosis.
Management and Treatment
Management of ACC is challenging due to its infiltrative nature.
Standard treatment includes:
- Wide surgical excision with negative margins- Adjuvant radiotherapy, particularly in cases with perineural invasion or close margins
- Neck dissection is not routinely performed unless nodal disease is present
Chemotherapy has limited efficacy and is generally reserved for advanced or metastatic disease.
Prognosis
ACC is notable for its paradoxical prognosis:
- Relatively good short-term survival
- Poor long-term outcomes due to late local recurrence and distant metastasis (commonly lungs and bone)
Five-year survival rates may appear favorable, but 10- and 20-year survival rates decline significantly. Lifelong follow-up is recommended.
Role of Dental and Medical Professionals
Dental professionals play a vital role in:
- Early detection of palatal and minor salivary gland tumors- Recognition of pain or paresthesia as warning signs
- Prompt referral for biopsy and imaging
- Long-term monitoring for recurrence
For students, ACC illustrates the importance of understanding tumor biology beyond histologic grade.
Conclusion
Adenoid Cystic Carcinoma is a distinctive salivary gland malignancy marked by perineural invasion, insidious progression, and late metastasis. Despite its slow growth, ACC requires aggressive initial management and prolonged surveillance. For dental and medical professionals, early recognition and interdisciplinary care are essential to improving long-term patient outcomes.