Parotid pleomorphic and non-pleomorphic adenomas: a mono-institutional series of 512 patients

Purpose: Pleomorphic adenoma (PA) is the most common benign parotid tumor, with a well-known propensity to recur. Many factors have been advocated as prognostic, but there is no consensus on how they affect local control. We studied how PA recurrence-free survival (RFS) may be affected by the most relevant risk factors in a time-to-event analysis, comparing them with those observed in a population of non-PA (NPA). Methods: Patients undergoing parotidectomy for benign lesions between 2002 and 2018 in a single academic tertiary referral center were included. A description of patients, tumors, and treatment characteristics was performed, highlighting differences between PA and NPA. Analysis of PA RFS and relative risk factors was also conducted. Results: Eight hundred fifty patients underwent parotidectomy for benign lesions, 455 (53.5%) for PA and 57 (6.7%) for NPA. Significant differences between PA and NPA were age at surgery, surgical procedure, and resection margins. Recurrence occurred in 3.1% of PA, with a median disease-free interval of 54 months. 2-, 5-, and 10-year RFS were 99.2, 98.5, and 93.9%, respectively. Age < 18 years (HR = 31.31, p < 0.001), intraoperative tumor spillage (HR = 6.57, p = 0.041), extensive pseudo-capsule interruption (HR = 5.85, p = 0.023), and resection margins < 1 mm (HR = 3.16, p = 0.085) were associated with RFS. Conclusion: Patients affected by NPA were significantly older and treated with more conservative surgical procedures compared to those with PA. In PA, younger age, major pseudo-capsule defects, and surgical margins were the most relevant factors affecting local control. These results confirm the importance of an appropriate surgical management and long-term follow-up in PA.