Thyroid cancer is the most common endocrine malignancy and consists of a diverse group of histological entities¹. Although ranging from indolent and well differentiated to aggressive and rapidly developing carcinomas, advanced disease may present in each histological subtype. Even though the characteristics of advanced thyroid cancer are recognized intuitively by experienced surgeons in the field, a common definition among scientific societies is yet to be reached². General definitions of advanced disease are included in the broader management guidelines for each cancer subtype, such as the American Thyroid Association (ATA) guidelines for differentiated thyroid cancer (DTC)³, medullary thyroid cancer (MTC)⁴, and anaplastic thyroid cancer (ATC)⁵. In the European setting, the 2019 European Society of Medical Oncology (ESMO) guideline⁶ on thyroid cancer includes a subsection on the management of advanced disease for each thyroid cancer type. Given the recent progress and new developments in targeted therapy, depending on the genetic alterations of the tumour, new interest has emerged in better defining advanced thyroid disease and selecting candidates for tailored therapy, either in an adjuvant systemic or neoadjuvant setting. This is reflected in the most recent published position statement by the American Head and Neck Society (AHNS) and International Thyroid Oncology Group⁷, as well as the clinical practice guidelines update by ESMO for the use of systemic therapy in advanced thyroid cancer⁸. Nevertheless, existing efforts to define advanced thyroid cancer and to produce management guidelines have been burdened by a common denominator, the lack of high-quality evidence, especially regarding definitions and surgical management.

Introduction: Currently, there is no consensus on the indication of prophylactic surgery of the nodal compartments in the treatment of medullary thyroid carcinoma (MTC). The aim of our study was to perform a correlation study between preoperative calcitonin (basalCT) values and lymph node involvement to establish a criterion on which to base prophylactic surgery in these patients.Material and Methods: We conducted an observational, retrospective and multicentre study with 29 hospitals. Patients over 18 years of age with a diagnosis of MTC with a pre‐surgical calcitonin registry were included. The minimum surgery in all patients had to have been total thyroidectomy (TT) with central compartment lymph node dissection (CCLND). Receiver operating characteristic (ROC) curve analysis was used to establish basalCT cut‐off values as predictors of postoperative lymph node involvement.Results: A total of 244 patients were included. Baseline calcitonin (basalCT) was a good predictor of nodal involvement (AUC 0.718 and 95%CI 0.66–0.978). Heritability was identified as a preoperative factor correlated with baseline tumour CT values (p = 0.000). With a probability of lymph node involvement below 10%, new cut‐off points were established. A prophylactic bilateral lateral lymph node dissection in sporadic tumours should be performed at a basalCT > 600 pg/mL; in the case of RET‐mutated tumours this value would be 200 pg/mL.Conclusion: The baseline CT value is a good predictor of postoperative lymph node involvement in MTC, however, cut‐off points should depent on the hereditary nature of the tumour.