Molecular Profiling for Bethesda III to VI Nodules: Results of a Multicenter International Retrospective Study.

Objective: Molecular testing is a well-established tool that assists in the management of thyroid nodules. We describe our experience using molecular testing of thyroid nodules with Bethesda III to VI cytology.

Methods: This is a retrospective multicenter, multinational study of thyroid nodules that underwent preoperative molecular profiling with ThyGenX/ThyGeNEXT or ThyroSeq V3 between 2015 and 2022. The clinical characteristics and mutational profiles of tumors were compared. Collected data included demographics, cytology results, surgical pathology, and molecular alterations. Molecular alterations were categorized into 3 main phenotypes: BRAF-like, RAS-like, and non-BRAF-non-RAS (NBNR).

Results: Overall, 784 patients who had surgery were included, of which 603 (76.2%) were females. The most common histologic type was papillary thyroid cancer (PTC) with 727 (91.9%) cases. In total, 205 (28.2%) cases showed an aggressive subtype of PTC (eg, tall cell and hobnail). BRAF-like alterations were most likely to be found in Bethesda V and VI nodules and show extrathyroidal extension (ETE), nodal disease, and/or aggressive subtypes of PTC (P < .001 for all). RAS-like alterations were more commonly found in Bethesda III and IV nodules and were less likely to show ETE, nodal disease, and/or aggressive histology (P < .001 for all). NBNR alterations were more commonly found in Bethesda III and IV nodules and were less likely to show ETE, nodal disease, and/or aggressive subtypes of PTC. However, they were rarely but significantly associated with poorly differentiated thyroid cancer (P < .005).

Conclusion: Molecular testing of thyroid nodules can help determine the likelihood of malignancy and classify nodules into several tumor phenotypes, predicting their behaviors and potentially allowing for a more tailored treatment. NBNR alterations should be managed with caution.