Clinical and pathologic prognostic features in acinic cell carcinoma of the parotid gland.

Background: To the authors' knowledge, the indications for adjuvant treatment in acinic cell carcinoma (AciCC) of the parotid gland have not been elucidated to date. The aim of the current study was to determine patterns of failure and adverse prognostic features.

Methods: Between March of 1989 and August of 2006, 35 patients underwent surgery at Memorial Sloan-Kettering Cancer Center for AciCC of the parotid gland and had their clinical and pathologic features retrospectively analyzed at the primary site. All cases were reviewed by 2 head and neck pathologists. Five-year estimates of survival outcomes were performed, followed by univariate analysis of potential prognostic features.

Results: The T classifications were as follows: T1 in 46% of patients, T2 in 23% of patients, T3 in 18% of patients, and T4 in 9% of patients. Three patients had cervical lymph node involvement. All patients underwent surgery as their primary treatment. Approximately 63% of patients (n = 22) received radiation treatment. The median follow-up time for surviving patients was 59.9 months. Five-year estimates of disease-free survival (DFS), overall survival (OS), and local control were 85%, 90%, and 90%, respectively. Of the clinical variables tested, clinical extracapsular extension (ECE), facial nerve sacrifice, and lymph node involvement were found to be significantly associated with a detriment in DFS and OS (P < .05). Positive surgical margins, histologic ECE, >2 mitoses per 10 high-power fields (HPF), atypical mitosis, vascular invasion, perineural invasion, pleomorphism, and necrosis were associated with adverse DFS (P < .05). All of these variables except for vascular invasion (P = .377) and perineural invasion (P = .07) were associated with OS. If high-grade tumors were defined on the basis of high mitotic activity (>2 mitoses/10 HPF) and/or tumor necrosis, high-grade carcinomas had a significantly lower DFS and OS (P = .001).

Conclusions: AciCC had a low treatment failure rate, and a large number of patients could be considered candidates for surgery only. A histologic grading system was devised to help stratify patients for adjuvant treatment.