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Background: The follicular variant of papillary thyroid carcinoma (FVPTC) presents distinct histologic subtypes and molecular genotyping. The preoperative diagnosis of FVPTC through fine-needle aspiration cytology (FNAC) is challenging.

Methods: We reviewed 59 archival thyroid FNAC specimens of surgically confirmed FVPTC according to histologic subtype: encapsulated FVPTC (n=30) and infiltrative FVPTC (n=29). Galectin-3 immunostaining and molecular analyses for BRAF and three RAS genes (NRAS, HRAS, and KRAS) were performed.

Results: FNAC diagnoses of FVPTC included benign (5%), atypia of undetermined significance (19%), follicular neoplasm/suspicious for follicular neoplasm (14%), suspicious for PTC (29%), and PTC (34%). Galectin-3 immunostaining was positive in 50% of FNAC specimens. A BRAF mutation was found only in 14 (24%) tumors with the FNAC diagnosis of PTC or …