Clinical impact of the new SIAPEC-IAP classification on the indeterminate category of thyroid nodules

The increasing frequency in the diagnosis of thyroid nodules has raised a growing interest in the search for new diagnostic tools to better select patients deserving surgery. In 2014, the major Italian Societies involved in the field drafted a new cytological classification, to better stratify pre-surgical risk of thyroid cancer, especially for the indeterminate category, split into TIR3A and TIR3B subclasses, associated to different therapeutic decisions.

This retrospective cross-sectional survey analyzed thyroid fine-needle aspiration biopsy performed at our outpatient clinic before and after the introduction of the new SIAPEC-IAP consensus in May 2014.

8956 thyroid nodules were included in the analysis: 5692 were evaluated according to the old classification and 3264 according to the new one. The new criteria caused the overall prevalence of TIR3 to increase from 6.1 to 20.1%. Of those, 10.7 and 9.4% were included in the TIR3A and TIR3B subgroups, respectively. Each of the 213 TIR3B nodules underwent surgery and 86 (40.4%) were diagnosed as thyroid cancer, while among the 349 TIR3A nodules, only 15 of the 60 that underwent surgery were found to be thyroid cancer.

This analysis shows that the new SIAPEC-IAC criteria significantly increased the proportion of the overall TIR3 diagnosis. The division of TIR3 nodules into two subgroups (A and B) allowed a better evaluation of the oncologic risk and a better selection of patients to be referred to surgery.