Evaluating the role of metaplasia in the cytologic diagnosis of pleomorphic adenoma: A multi‐institutional study of 253 cases

Background Pleomorphic adenoma (PA) is the most common benign salivary gland neoplasm detected by fine‐needle aspiration (FNA). However, metaplastic changes within PA can complicate its cytologic interpretation. This study evaluates the impact of metaplasia on the FNA interpretation in a large, multi‐institutional cohort. Methods A two‐armed study design was employed: one included 200 consecutive PA resections and the corresponding FNAs, and the second included 53 PA cases with known metaplastic features identified by cytologic or pathologic review. Results Histologic assessment revealed metaplasia in 16% of the 200 PA cases. Although the majority (83%) were cytologically classified as Neoplasm: Benign, indeterminate diagnoses were more common in cases with metaplasia (25%) than in those without (15.5%). Squamous metaplasia was frequently interpreted as indeterminate relative to other types of metaplasia, and a statistical trend was observed between the extent of metaplasia and indeterminate categorization. In the multicenter arm, FNA cases with metaplasia were more frequently interpreted as indeterminate compared to FNA cases without metaplasia (61.8% vs. 15.8%, p < .01). Conclusions Metaplastic change in PA can pose diagnostic challenges. Although most FNA cases with limited metaplastic features are appropriately classified, extensive metaplasia is more likely to result in an indeterminate interpretation.