BRAF^K601E Mutation in a Follicular Thyroid Adenoma: A Case Report

BRAF mutations represent the most common genetic alteration in papillary thyroid carcinoma (PTC). The p.V600E mutation is specific for the classic and tall-cell variants of PTC and has been associated with a more aggressive biologic behavior. On the other hand, the p.K601E mutation is peculiar to the follicular variant of PTC, and seems to be a favorable prognostic indicator. A 12-year-old boy presented with a 10-mm left-sided thyroid nodule. Fine-needle aspiration cytology reported the lesion as suspicious for a follicular neoplasm (Bethesda category IV). The patient underwent lobectomy, and histopathology revealed a follicular adenoma with normal surrounding tissue. The cytological smear was found to be positive for BRAF p.K601E mutation, and this was later confirmed on the corresponding paraffin block. This case was independently revised by 4 expert pathologists, all of whom confirmed the benign nature of the thyroid lesion. This article describes the presence of a BRAF mutation in a benign thyroid lesion. To the authors' knowledge, this is the fourth case of follicular adenoma carrying BRAF^K601E reported in literature to date. BRAF^K601E mutation can occur in benign thyroid lesions. This finding, in the context of the current literature and the recently proposed reclassification of the noninvasive encapsulated follicular variant of papillary thyroid carcinoma into a benign lesion, confirms the importance of preoperative BRAF p.K601E testing in offering patients a tailored treatment plan and avoiding overtreatment.