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

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).

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.

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.

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.