ATA risk classification of papillary thyroid cancer according to pre-surgery cytology

Abstract Objective To compare ATA risk staging of histologically proven Papillary Thyroid Cancer (PTCs) in patients who received a pre-surgery cytologic result of either Indeterminate-Thyroid-Nodules (ITN, Bethesda III/IV) or suspicious for malignancy/malignant (TIR4/5, Bethesda V/VI). Methods Clinical, ultrasonographic, cytological data from patients with histologically diagnosed PTC were retrospectively collected. Results Patients were stratified according to the pre-operative FNAC into two groups, 51 ITNs (TIR3A/3B) and 118 suspicious/malignant (TIR4/5). Male/female ratio, age, pre-surgery TSH level were similar between the two groups. At ultrasound, TIR 4/5 nodules were significantly more frequently hypoechoic (p=0.037), with irregular margins (p=0.041) and with microcalcifications (p=0.020) and were more frequently classified as high-risk according to EU-TIRADS (p=0.021). At histology, the follicular PTC subtype was significantly more prevalent among ITNs while classical PTC subtype was more frequent in TIR4/5 group (p=0.002). In TIR4/5 group a higher rate of focal vascular invasion (p<0.001) and neck lymph-node metastasis (p=0.028) was observed. Intermediate-risk category according to ATA was significantly more frequent in TIR4/5 group while low-risk category was more frequently found among ITNs (p=0.021), with a higher number of patients receiving radioiodine in TIR4/5 group (p=0.002). At multivariate logistic regression, having a TIR4/5 cytology was associated with a significant risk of having a higher ATA risk classification as compared to ITN [OR 4.6 (95% C.I. 1.523-14.007), p=0.007], independently from pre-surgery findings (nodule size at ultrasound, sex, age and EU-TIRADS score). Conclusions PTCs recorded among ITNs are likely less aggressive and are generally assessed as at lower risk according to ATA classification.