Subjects

This study was approved by the ethic committee of our institution.

Patients 18 years-old or older, consecutively treated and followed prospectively at our institution between December 2012 and December 2018, who met the following criteria were initially selected: (i) diagnosis of classic or WL-PTC; (ii) subjected to total thyroidectomy, with neck dissection performed only with evidence of clinically apparent nodal disease detected at clinical examination, preoperative neck ultrasound (US), or during intra-operative inspection by the surgeon; and (iii) followed for at least 6 months. Nodal disease was classified in low and high volume according to 2015 American Thyroid Association (ATA) guideline ( 7 ). All biopsies were reviewed by an experienced pathologist (A.S.).

The need for radioiodine (RAI) was defined in each patient following the recommendations of the 2009 ATA guidelines until December 2015, and the 2015 ATA guidelines were followed starting January 2016 ( 7 , 8 ). Patients were classified according to the ATA 2015 recurrence risk category (low, intermediate and high) as well as the eighth edition of the AJCC/UICC staging system (I, II, III and IV) based on the preoperative neck US, intra-operative findings and final surgical pathology report ( 7 , 9 ).

Patients who met any of the following criteria were excluded: (i) partial thyroidectomy; (ii) absence of or incomplete surgical pathology report; (iii) follow-up of less than 6 months; or (iv) Tg, TgAb or neck US not performed during follow-up.