Atypia of undetermined significance on thyroid fine needle aspiration – risk factors for malignancy

Objectives: This study is designed to determine the clinical predictors of malignancy in the atypia of undetermined significance (AUS) category resulted from thyroid fine needle aspiration (FNA). Design: Retrospective cohort study. Setting: Dong-A University Medical Center, Busan, Korea. Participants: Sixty-two patients who underwent thyroid surgery from January 2010 to December 2013, following a diagnosis of AUS from preoperative thyroid FNA. Main outcome measures: We investigated the age, gender, maximum size and site of the nodules, ultrasonographic findings, cytological features, BRAF gene mutation, surgical method, number of AUS on repeated FNA and final pathologic results. Results: Forty-one of sixty-two patients underwent total thyroidectomy and the rest had lobectomy. The final pathologic results were 41 malignancies and 21 benign diseases. Nodules less than 1.5 cm, ultrasonographic findings suggestive of malignancy were risk factors for malignancy on univariated analysis (P < 0.001). Multivariated analysis showed that nodules less than 1.5 cm, ultrasonographic findings suggestive of malignancy and more than 2 results of atypia from repeated FNAs were significant risk factors for malignancy (P < 0.001). A BRAF gene mutation analysis was performed in 38 patients, and 13 patients had the mutation. All patients with the BRAF gene mutation had been diagnosed with papillary thyroid cancer (P > 0.05). Conclusions: We recommend close observation or diagnostic surgery in patients with nodules <1.5 cm and with two or more malignant ultrasound feature and a BRAF mutation, or with two or more AUS findings on repeated FNAs.