The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), which attempts to standardize reporting and cytological criteria for fine-needle aspiration of thyroid nodules and was first introduced in 2009, has been updated. Although much of the original TBSRTC remains the same, several “enhancements” have been introduced in the 2017 version based on new data and developments in the field. The 2017 revision reaffirms that every thyroid FNA report should begin with one of six diagnostic categories, the names of which remain unchanged since they were first introduced: nondiagnostic or unsatisfactory; benign; atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS); follicular neoplasm or suspicious for a follicular neoplasm; suspicious for malignancy; and malignant. In the frst edition of TBSRTC, the implied risk of malignancy (MOP) for each diagnostic category was calculated and provided as a range based on a review of the literature at that time: 0–3% for benign, ~5–15% for atypia of undetermined signifcance (AUS) or follicular lesion of undetermined signifcance (FLUS), 15–30% for follicular neoplasm or suspicious for follicular neoplasm, 60–75% for suspicious for malignancy, and 97–99% for the malignant category. In the second edition, these ranges have been revised, especially for the so-called “indeterminate” categories, representing estimates calculated primarily from studies of large case cohorts and meta-analyses of ultrasound-guided thyroid FNA published after 2007. Notably, the new document reinterprets the previous version in one major way, and that is TBSRTC’s careful accommodation of the new noncancer category of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) tumors, which prior to April 2016 were categorized as thyroid cancer. NIFTP tumors have nuclear changes on cytologic evaluation that are identical to other forms of thyroid cancer, but on close long-term clinical follow-up they do not appear to recur or metastasize, and therefore, they do not behave clinically like thyroid cancer. NIFTP tumors typically fall into categories 3, 4, or 5, and can only be diagnosed as “not cancer” after a full surgical excision is performed and the entire tumor specimen is examined under a microscope. There have also been a number of other enhancements with the 2017 update: • The option of molecular testing in the standard management of AUS/FLUS and FN/SFN has been included. • The definition and diagnostic criteria for FN/SFN has been modified: cases demonstrating mild nuclear changes associated with papillary thyroid carcinoma are now included. The definition and diagnostic criteria for the papillary thyroid carcinoma subset of the malignant category now suggest limiting use to cases with “classical” features of papillary thyroid carcinoma. TBSRTC is now the most common classification worldwide for the reporting of thyroid FNA specimens. In view of this, ABSTRACTS 92 MATERIA MEDICA • Vol. 34 • Issue 1, suplement 1 • april 2018. new suggestions will be useful for various aspects of thyroid FNA including nomenclature, differential diagnosis, the potential impact of NIFTP on the indeterminate diagnostic categories, utility of molecular and IHC markers, and clinical management.

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.