The presence of papillary features in thyroid nodules diagnosed as atypia of undetermined significance or follicular lesion of undetermined significance increases cancer risk and should influence treatment.

BACKGROUND: The objective of this study was to evaluate the influence of papillary features on risk of malignancy (ROM) within the Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance (AUS-FLUS) Bethesda System for Reporting Thyroid Cytopathology (BSRTC) diagnostic category.

METHODS: A Retrospective review of cases with an AUS-FLUS diagnosis that underwent a thyroidectomy was carried out, and cases were subcategorized based upon the presence of papillary features.

RESULTS: For the entire study population there were 93 (22%) of 427 FNAB specimens that had an AUS-FLUS diagnosis, and a 32% associated ROM. Papillary features were identified in 44 FNAB specimens (47% of the AUS-FLUS cases or 10% of the entire study population), and when present had a 45% ROM. The 49 FNAB specimens (53%) that did not exhibit papillary features had a significantly lower ROM (20%) than those that did have papillary features (p = 0.0069).

CONCLUSIONS: The presence of papillary features in a thyroid FNAB with an AUS-FLUS diagnosis is common, and is associated with a higher ROM than is currently suggested by the BSRTC.