**5. Conclusions**

In this study, we compared the performances of the ACR and EU-TIRADS systems, showing the statistically significant higher specificity of the ACR and a comparable sensitivity, PPV, and NPV. The coupled use of the ACR or EU-TIRADS with the cytological class did not improve the diagnostic performance in identifying malignant nodules. However, the combination of specific ultrasound features with cytological class might help in the diagnosis of malignant nodules, especially with an indeterminate for the malignancy pathological report.

**Author Contributions:** Conceptualization, D.S., G.C., S.G., V.L. and F.P.; Data curation, D.S., G.C., D.L., D.F., F.V., C.D.B., S.G., V.L. and F.P.; Formal analysis, D.S., G.C., S.G., V.L. and F.P.; Funding acquisition, F.P.; Methodology, F.P.; Writing—original draft, D.S., G.C., S.G., V.L. and F.P.; Writing review and editing, D.S., G.C., S.G., V.L. and F.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the grant Ricerca Finalizzata 2019-GR-2019-12368592 (Italian Minister of Health, Ministero della Salute).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the ASST Monza Ethical Board (October 2016, 27102016).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are more extensively available in Leni, D.; Seminati, D.; Fior, D.; Vacirca, F.; Capitoli, G.; Cazzaniga, L.; Di Bella, C.; L'Imperio, V.; Galimberti, S.; Pagni, F. Diagnostic Performances of the ACR-TIRADS System in Thyroid Nodules Triage: A Prospective Single Center Study. Cancers 2021, 13, 2230. https://doi.org/10.3390/cancers13092230.

**Conflicts of Interest:** The authors do not have any conflicts of interest to declare.
