The American Thyroid Association risk classification of papillary thyroid cancer according to presurgery cytology

To compare the American Thyroid Association (ATA) risk staging of histologically proven papillary thyroid cancer (PTC) in patients who received a presurgery cytologic result of either indeterminate thyroid nodules (ITNs, Bethesda III/IV) or suspicious for malignancy/malignant (TIR 4/5, Bethesda V/VI).

Clinical, ultrasonographic, cytological data from patients with histologically diagnosed PTC were retrospectively collected.

Patients were stratified according to the preoperative fine-needle aspiration cytology into 2 groups: 51 ITNs (TIR3A/3B) and 118 suspicious/malignant (TIR 4/5). Male/female ratio, age, and presurgery TSH level were similar between the 2 groups. At ultrasound, TIR 4/5 nodules were significantly more frequently hypoechoic (P = .037), with irregular margins (P = .041), and with microcalcifications (P = .020) and were more frequently classified as high-risk according to the European Thyroid Imaging and Reporting Data System (EU-TIRADS; P = .021). At histology, the follicular PTC subtype was significantly more prevalent among ITNs while classical PTC subtype was more frequent in TIR 4/5 group (P = .002). In TIR 4/5 group, a higher rate of focal vascular invasion (P < .001) and neck lymph node metastasis (P = .028) was observed. Intermediate-risk category according to ATA was significantly more frequent in TIR 4/5 group while low-risk category was more frequently found among ITNs (P = .021), with a higher number of patients receiving radioiodine in TIR 4/5 group (P = .002). At multivariate logistic regression, having a TIR 4/5 cytology was associated with a significant risk of having a higher ATA risk classification as compared to ITN (OR 4.6 [95% CI 1.523-14.007], P = .007), independently from presurgery findings (nodule size at ultrasound, sex, age, and EU-TIRADS score).

Papillary thyroid cancers recorded among ITNs are likely less aggressive and are generally assessed as at lower risk according to ATA classification.