The influence of papillary features on the risk of malignancy in thyroid nodules diagnosed as atypia of undetermined significance or follicular lesion of undetermined significance

Background: The objective of this study was to the assess the risk of malignancy in thyroid lesions that were diagnosed as AUS/FLUS when using a novel cytology subclassification system that is based on the presence or absence of papillary features. Methods: AUS/FLUS case cytology was re-reviewed and subclassified into minor or major concern groups based upon the absence or presence of papillary features, respectively. The risk of malignancy (ROM) was calculated and compared between the two groups. Inter-pathologist agreement in case subclassification was also measured. Results: The minor concern group had a 12.6% associated ROM, while the major concern group had a signifi-cantly higher ROM (58.4%), (P < 0.001). Based on 108 cases, the inter-pathologist agreement in case subclas-sification was 79%, and the kappa value was 0.47. Conclusions: The identification of papillary features significantly increases the ROM in thyroid lesions with an AUS/FLUS diagnosis.