Factors Predicting Thyroid Malignancy in Fine Needle Aspiration Biopsy Specimens Classified as Atypia of Uncertain Significance/Follicular Lesion of Uncertain Significance

Abstract

The atypia of uncertain significance/follicular lesion of uncertain significance (AUS/FLUS) category of the Bethesda system for reporting thyroid cytopathology for fine needle aspiration biopsy (FNAB) has a predicted incidence of malignancy from 5 to 15 per cent. The literature has reported that suspicious ultrasound (SUS) characteristics can assist in predicting malignancy in thyroid biopsies. Some research suggests further subdivision of AUS/FLUS into nuclear atypia predominant or follicular predominant. We hypothesized that the rate of malignancy would be higher in AUS/FLUS biopsies with SUS characteristics and in the AUS/FLUS subset classified as nuclear atypia predominant. We performed a four-year retrospective analysis of patients who underwent FNAB classified as AUS/FLUS and who subsequently underwent thyroidectomy from October 2008–October 2012. A total of 3839 thyroid FNAB were performed over the four-year period, of which 342 received AUS/FLUS classification. Of these, we identified 119 patients who underwent thyroidectomy, of which 27 (23%) malignancies were identified. Reported cytology (nuclear atypia vs follicular predominant) did not differ between patients with and without carcinomas (P = 0.33). Suspicious ultrasound appearance failed to be significantly associated with an underlying carcinoma (P = 0.14); although, nearly 70 per cent of malignancies displayed SUS compared with 50 per cent within the benign group. Ultrasound seems to have no additional value in predicting malignancy in the AUS/FLUS categorization. Further subcategorization did not aid in risk stratification of this indeterminate category. This may suggest an expanded role for ancillary technologies such as molecular markers in this challenging Bethesda system for reporting thyroid cytopathology class. Further study of these findings is warranted.