Background: Bethesda III and IV thyroid nodules, which fall under the category of indeterminate cytology, pose challenges in clinical decision-making due to their ambiguous risk of malignancy. Molecular testing has been increasingly employed to aid risk stratification and optimize the extent of surgical intervention. Methods: A retrospective review of 410 patients with Bethesda III and IV thyroid nodules who underwent thyroid surgery at McGill University teaching hospitals between January 2016 and April 2022. Patients were grouped based on whether or not they underwent preoperative molecular testing. Data were collected on demographic variables, histopathologic diagnosis, mutation profiles, and surgical outcomes. The primary outcome was to assess for concordance between surgical intervention and final pathology in both groups, with a focus on identifying optimal versus suboptimal management. Optimal management is defined as surgery appropriate to the aggressiveness of disease, meaning a hemi-thyroidectomy for a non-aggressive malignancy, total thyroidectomy for an aggressive malignancy, and no surgery for a benign nodule. Furthermore, suboptimal management includes unnecessary surgery or incorrect surgery for the level of aggressivity of the nodule. Results: Among the 410 patients, 203 underwent molecular testing, while 207 did not. Of those who underwent molecular testing, 117 had Bethesda III nodules and 86 had Bethesda IV nodules. In the non-tested group, 129 and 78 patients had Bethesda III and IV nodules, respectively. Optimal surgical intervention was achieved in 67.5% of patients who underwent molecular testing, compared with 25.1% in those who did not (p < 0.001). Subgroup analysis revealed that 61.5% of Bethesda III nodules with molecular testing received optimal care versus 21.0% of those without testing. In the Bethesda IV cohort, optimal surgery was achieved in 75.6% with testing versus 32.1% without. Among the suboptimally managed patients, 70.1% (155/221) were from the group that did not undergo molecular testing. In addition, molecular testing identified aggressive mutations such as BRAF V600E and TERT promoter mutations more frequently in Bethesda III nodules, while RAS-like mutations, associated with indolent behavior, predominated in Bethesda IV nodules. Conclusions: In this study, molecular testing significantly improved risk stratification and the likelihood of optimal surgical management in patients with Bethesda III and IV thyroid nodules. Incorporating molecular diagnostics into the standard preoperative workflow may enhance patient care, reduce unnecessary surgeries, and optimize the extent of surgery. Future studies should evaluate the cost-effectiveness and broader implementation of molecular testing in diverse healthcare settings.

Background: Thyroid cancer is the most common endocrine malignancy, and accurate diagnosis is crucial for effective management. Fine needle aspiration cytology, guided by the Bethesda System for Reporting Thyroid Cytopathology, categorizes thyroid nodules into six categories, with Bethesda III and IV representing indeterminate diagnoses that pose significant challenges for clinical decision-making. Understanding the molecular profiles of these categories may enhance diagnostic accuracy and guide treatment strategies. Methods: This study retrospectively analyzed data from 217 patients with Bethesda III and IV thyroid nodules who underwent ThyroSeq v3 molecular testing followed by thyroid surgery at McGill University teaching hospitals. The analysis focused on the presence of specific molecular mutations, copy number alterations (CNAs), and gene expression profiles (GEPs) within these nodules. The relationship between these molecular findings and the clinico-pathological features of the patients was also examined. Results: This study identified notable differences in the molecular landscape of Bethesda III and IV thyroid nodules. Bethesda IV nodules exhibited a higher prevalence of CNAs and distinct GEPs compared to Bethesda III nodules. Interestingly, the BRAFV600E mutation was found exclusively in Bethesda III nodules, which correlated with more aggressive malignant behavior. These findings underscore the potential of molecular profiling to differentiate between the clinical behaviors of these indeterminate nodule categories. Conclusions: Molecular profiling, including the assessment of CNAs, GEPs, and specific mutations like BRAFV600E, provides valuable insights into the nature of Bethesda III and IV thyroid nodules. The distinct molecular characteristics observed between these categories suggest that such profiling could be instrumental in improving diagnostic accuracy and tailoring treatment approaches, ultimately enhancing patient outcomes in thyroid cancer management.