Core Outcome Set of the Surgical Treatment of Differentiated Thyroid Carcinoma: International Consensus by Delphi Study

<b><i>Background:</i></b> No international consensus exists on the selection and reporting of outcomes after differentiated thyroid cancer (DTC) surgery, hindering assessment of new treatments and guideline formation. Therefore, we aimed to develop an international core outcome set (COS) to be measured and reported in future studies investigating surgical treatment for DTC, as well as in clinical practice. <b><i>Methods:</i></b> COS development consisted of three phases: (1) collecting an initial outcome list through a literature review, (2) a two-round international Delphi process with experts and patient representatives, and (3) international expert panel meeting to finalize the COS. A steering committee including experts from varying medical (sub-)specialties and a patient representative from the Dutch Thyroid Patient Organization advised on the study protocol, Delphi rounds, and expert panel meeting. Experts were identified through scientific associations, international guidelines on DTC, ClinicalTrials.gov, and last authors of key studies and suggestions from the steering committee. The outcomes from the literature review were presented in successive rounds to experts and patient representatives to assess their importance for inclusion in the DTC surgical COS. Delphi results were analyzed for each stakeholder group on a 1-9 Likert scale. Consensus-in was defined as 70% or more of participants in both stakeholder groups rating the outcome 7-9 or 90% in one group. Consensus-out was defined as 70% or more in both groups rating the outcome 1-3. Consensus-out required agreement across both groups. <b><i>Results:</i></b> A total of 125 experts and 7 patient representatives from 35 countries across 5 continents completed all rounds. After two rounds, consensus was reached for 17 outcomes. Of these, 13 outcomes were ratified during the expert panel meeting: recurrence, persistent disease, location of metastatic lymph nodes, number of retrieved metastatic lymph nodes, postoperative thyroglobulin levels, surgical completeness, permanent recurrent laryngeal nerve paralysis due to surgery, permanent postoperative hypoparathyroidism, 30-day postoperative complication rate, accidental intraoperative injury to adjacent organ, unplanned reoperation rate, 30-day postoperative mortality, and quality of life. <b><i>Conclusions:</i></b> This international consensus on the COS for DTC surgery promotes consistent and appropriate outcome selection in clinical practice and research and may be incorporated into future study designs. Future steps include defining some outcomes.