Clinicopathologic Characteristics and Prognostic Factors of Primary and Recurrent Pleomorphic Adenoma: A Single Institution Retrospective Study of 705 Cases.

Although pleomorphic adenoma (PA) is benign, it may recur and prompt further treatment with radiotherapy (RT). This study investigated the prognostic features of primary and recurrent PAs. A total of 705 PAs (613 primary and 92 recurrent) were analyzed. The following parameters: age, site and size, status of resection, histologic features, and clinical management were documented and correlated with recurrence-free survival. For primary PAs: The mean patient age was 50 years (female/male: 2/1), the median size was 2.1 cm (range: 0.5 to 9.0 cm), and the most common location was the parotid (92%). Tumors showed the following: complete encapsulation (25%), involvement of the surrounding salivary gland/fat (74%), hypercellularity (26%), ≥10 pseudopods (15%), squamous metaplasia (43%), mitoses (49%), intravascular tumor deposit (n=1), close proximity to nerves (n=2), positive margin (15%), and suboptimal resection (2%). The recurrence rate was 3.4% and malignant transformation was <1%. On univariate analysis, age below 30, mitosis ≥3/10 HPFs, squamous metaplasia, hypercellularity, and suboptimal resection correlated with recurrence-free survival. On multivariate analysis, only age below 30, mitosis ≥3/10 HPF and suboptimal resection predicted recurrence. For recurrent PAs: The resected primary PAs were fragmented in 58%. Forty-eight percent of patients had subsequent recurrences, mostly within 10 years, and 1 patient developed a subsequent malignant transformation. Forty-two percent of patients received RT. On univariate analysis, only RT was associated with better outcome (P=0.033). Young age, high mitoses, and specimen integrity predicted recurrence in primary PA. Recurrent PAs are difficult to eradicate, and 48% of these recurred for the second time, mostly within 10 years.