Adenoid Cystic Carcinoma (ACC)
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Disease Description
Adenoid Cystic Carcinoma (ACC) Adenoid cystic carcinoma is a malignant neoplasm of epithelial salivary gland origin, predominantly of basal and myoepithelial cell origin. It occurs in minor and major salivary glands, including the parotid, submandibular, palatal, lacrimal, pharynx, laryngeal, skin, and breast glands among many other locations. It accounts for 4% of all salivary gland neoplasms and 7.5% of all epithelial salivary gland malignant neoplasms (5). There is no consensus in the literature on the most prevalent malignant salivary gland neoplasm of the oral cavity; some suggest adenoid cystic carcinoma to be the most common, while others show that mucoepidermoid carcinoma is the most common and yet a third group of reports suggest that polymorphous low grade adenocarcinoma is the most common (5, 7). It is not the intention of this author to favor any of these reports, but rather to state that adenoid cystic and mucoepidermoid carcinomas are more frequently diagnosed in our biopsy service than polymorphous low grade adenocarcinoma.
ACC occurs more commonly in middle-aged patients in the fourth to the sixth decade of life. However, it can occur in patients of all ages with slight predilection for occurrence in females. Although cases in the first decade and the tenth decade have been described, these extremes tend to be rare (5, 7-8). According to the AFIP’s records of their own diagnoses of ACC, 26.8% of cases occur in the parotid, 24% in the submandibular gland, 20.5% in the palate, 5% in the tongue, around 4% each in the lips and buccal mucosa and 1.2% in the sublingual gland (9).
Adenoid cystic carcinoma is a slow-growing neoplasm, persistent in growth and recurrence with a slow tendency for metastasis. It may present with local pain and facial nerve paralysis if affecting the parotid. Fixation to deeper structures and local invasion is common in the larger lesions. ACC of the palate may be covered with normal mucosa, making it indistinguishable from a benign salivary gland or soft tissue neoplasm. It may also be ulcerated, especially in larger lesions. It has a marked tendency for perineural invasion explaining the signs of pain or paresis (5-9).
Multiple genetic aberrations have been identified; one involves the loss of DNA copy number in chromosome 12q, and another involves deletion in 6q23 and 13q21 (6). Others show gain in chromosome 19 and deletion of chromosome 19q. Another study showed similarities in genetic abnormalities between adenoid cystic carcinoma and polymorphous low grade carcinoma involving chromosomes 12 and 6. These two malignant salivary gland neoplasms have other common clinical and histologic characteristics, making it difficult at times to differentiate between them.
Histologically, ACC is made up of infiltrative small, dark, uniform and basaloid cells with or without mitosis depending on the type. Three types have been described: cribriform pattern, solid pattern and tubular. Combinations of the three types are sometimes encountered in one neoplasm. Cribriform pattern is the most common type and is arranged in clusters and nests of epithelial cells with holes (spaces); thus, it is also known as a “Swiss cheese” pattern. The neoplastic cells are small, basaloid and uniform with little to no mitosis and no pleomorphism. It is clinically low-grade, behaving with multiple recurrences and a slow tendency for metastasis. The high-grade counterpart is also known as the solid type, where cells are arranged in nests with larger basaloid cells, pleomorphism and prevalent mitosis. Spaces within these clusters are usually scant or absent. This is a more aggressive type with a tendency for early metastasis. The tubular type is difficult to interpret since some believe is similar to the cribriform pattern in behavior. All three types have a tendency for perineural invasion (5-9).
Treatment
Complete surgical removal with wide clean margins of surrounding tissue is the treatment of choice. The patient elected a partial denture prosthesis with obturator. If there is histological evidence of perineural spread, nerves may be surgically followed to the skull base. Surgery combined with radiotherapy has been used, especially with recurrence or with surgical specimens involving the surgical margins. Radiotherapy alone has been used, but not effectively. Chemotherapy is used with metastasis. Prognosis is based on the clinical stage as well as the histology. Stages 1 and 2 have a much better 10-year survival rate than stages 3 and 4 (75% stages 1 and 2, 43% for stage 3 and 15% for stage 4). Histologically, the cribiform pattern has a better prognosis than the solid type. One study showed the 15-year survival rate for cribriform pattern cases to be 39%, compared with a 5% survival rate with the solid variant. The latter measured by tumor histologically made up of 30% solid ACC. These tumors tend to invade bone and metastasize to the lung. Because of the tendency for multiple recurrences and possible metastasis, long-term (20 years or more) follow-up is mandatory (5-9).
Referrences