Acinic cell carcinoma
Acinic cell carcinoma, also known as acinic cell adenocarcinoma, is a malignant epithelial neoplasm in which the neoplastic cells express acinar differentiation. By conventional use, the term acinic cell carcinoma is defined by cytologic differentiation towards serous acinar cells, as opposed to mucous acinar cells, whose characteristic feature is cytoplasmic periodic acid-Schiff (PAS)-positive zymogen-type secretory granules. In AFIP data of salivary gland neoplasms, acinic cell carcinoma is the third most common salivary gland epithelial neoplasm after mucoepidermoid carcinoma and adenocarcinoma, NOS. In these data, acinic cell carcinoma comprised 17% of primary malignant salivary gland tumors or about 6% of all salivary gland neoplasms; more than 80% occur in the parotid gland; women were affected more than men; and the mean age was 44 years. Other studies have reported a relative frequency of acinic cell carcinoma from 0% to 19% of malignant salivary gland neoplasms.
Clinically, patients typically present with a slowly enlarging mass in the parotid region. Pain is a symptom in more than 33% of patients. (Refer to the PDQ summary on Pain for more information.) For acinic cell carcinoma, staging is likely a better predictor of outcome than histologic grading. In a retrospective review of 90 cases, poor prognostic features included pain or fixation; gross invasion; and microscopic features of desmoplasia, atypia, or increased mitotic activity. Neither morphologic pattern nor cell composition was a predictive feature.
PLGA is a malignant epithelial tumor that is essentially limited to occurrence in minor salivary gland sites and is characterized by bland, uniform nuclear features; diverse but characteristic architecture; infiltrative growth; and perineural infiltration. In a series of 426 minor salivary gland tumors, PLGA represented 11% of all tumors and 26% of those that were malignant. In minor gland sites, PLGA is twice as frequent as adenoid cystic carcinoma, and among all benign and malignant salivary gland neoplasms, only pleomorphic adenoma and mucoepidermoid carcinoma are more common. In the AFIP case files, more than 60% of tumors occurred in the mucosa of either the soft or hard palates, approximately 16% occurred in the buccal mucosa, and 12% occurred in the upper lip. The average age of patients is reported to be 59 years, with 70% of patients between the ages of 50 and 79 years. The female to male ratio is about 2:1, a proportion greater than for malignant salivary gland tumors in general.[3,33]
PLGA typically presents as a firm, nontender swelling involving the mucosa of the hard and soft palates (i.e., it is often found at their junction), the cheek, or the upper lip. Discomfort, bleeding, telangiectasia, or ulceration of the overlying mucosa may occasionally occur. This salivary gland neoplasm typically runs a moderately indolent course. In a study of 40 cases with long-term follow-up, overall survival was 80% at 25 years. Because of the unpredictable behavior of the tumor, some investigators consider the qualifying term, low grade, to be misleading and instead prefer the term, polymorphous adenocarcinoma.