Thyroid nodules classified as atypia or follicular lesions of undetermined significance deserve further research: Analysis of 305 surgically confirmed nodules.

Objective: The objective of the present study was to determine the malignancy risk for nodules categorised as atypia or follicular lesions of undetermined significance atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) and to investigate the predictors of malignancy.

Methods: All nodules diagnosed as AUS/FLUS on fine needle aspiration (FNAs) performed between January 2011 and December 2015 were retrospectively reviewed. Clinical data, ultrasonographic features, follow-up data and the final pathological results were recorded. After further exclusion, only nodules that underwent surgical excision were included in the final analysis. The malignancy rate and the range of malignancy rates were calculated. Clinical and ultrasound features were examined to determine the predictors of malignancy.

Results: During the study period, FNA was performed on 9938 nodules, and 1019 (10.2%) nodules were diagnosed as AUS/FLUS. After further exclusion, 976 nodules were evaluated. After the initial diagnosis of AUS/FLUS, 139 (14.2%) patients underwent surgery, 518 (53.1%) had repeated FNAs. A total of 305 (31%) had undergone surgical excision at different time points. For surgically confirmed nodules, the malignancy rate after the initial FNA was 34.5% (the lower and upper thresholds for the malignancy rate were 19.3% and 66.3%, respectively), and 37.9% after the repeated FNA. No ultrasound feature was determined as a predictor, whereas age (>55 years) was a predictor for malignancy.

Conclusions: The overall malignancy rate for nodules diagnosed as AUS/FLUS and the malignancy rate for nodules that underwent repeated FNA after AUS/FLUS were higher than the expected malignancy rates of the National Cancer Institute. It is, therefore, suggested that the current recommendations should be reconsidered.