Molecular profiling for Bethesda III-VI nodules: results of a multicenter international retrospective study.

BACKGROUND: 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-VI cytology.

METHODS: Retrospective multicenter multinational study of thyroid nodules that underwent preoperative molecular profiling with ThyGenX/ThyGeNEXT or ThyroSeq V3 between 2015-2022. 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: 784 patients who had surgery were included, of which 603(76.2%) were females. The most common histological type was papillary thyroid cancer(PTC) with 727(91.9%) cases. In total 205 (28.2%) cases showed an aggressive subtype of PTC (e.g. tall cell, hobnail). BRAF-like mutations were most likely to be found in Bethesda 5 and 6 nodules and show extrathyroidal extension, nodal disease and/or aggressive subtypes of PTC(P<0.001 for all). RAS-like mutations were more commonly found in Bethesda 3 and 4 nodules, were less likely to show extrathyroidal extension, nodal disease and/or aggressive histology(P<0.001 for all). NBNR mutations were more commonly found in Bethesda 3 and 4 nodules, were less likely to show extrathyroidal extension, nodal disease and/or aggressive subtypes of PTC. However, they were rarely but significantly associated with poorly differentiated thyroid cancer(P<0.005).

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 mutations should be managed with caution.