Diagnostic value of molecular testing for evaluating thyroid nodules greater than 4 centimeters.

[BACKGROUND] Molecular testing (MT) aids in reducing unnecessary thyroidectomy for indeterminate thyroid nodules, primarily due to its high negative predictive value (NPV). However, its reliability in large nodules (≥4 ​cm), which carry a higher malignancy risk, remains unclear.

[METHODS] We performed a retrospective study of patients with thyroid nodules ≥4 ​cm who underwent fine-needle aspiration (FNA) at a tertiary care center from 2015 to 2023. Cytology was categorized using the Bethesda system. Molecular results (Afirma GEC and GSC) were matched with surgical pathology. Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was classified as malignant.

[RESULTS] A total of 231 patients were included (mean age 52 ​± ​16 years; 69.7 ​% female). The median nodule size was 5.0 ​cm (IQR: 4.4-5.8). Malignancy was identified in 28.1 ​% of cases. Malignancy rates by Bethesda category were 4.3 ​% (Bethesda II), 33.8 ​% (III), and 50.0 ​% (IV), all Bethesda V and VI nodules were malignant. Among 96 patients with Bethesda III or IV cytology, 79 (82.3 ​%) underwent MT, 30 with GEC and 47 with GSC. GEC yielded 91.7 ​% sensitivity, 33.3 ​% specificity, and NPV of 85.7 ​%. GSC showed 88.9 ​% sensitivity, 58.6 ​% specificity, and NPV of 89.5 ​%. Malignancy occurred in 40.0 ​% (GEC) and 38.3 ​% (GSC) of tested nodules. False negatives included anaplastic carcinoma, oncocytic carcinoma, and NIFTP. Mutation testing revealed malignancy in 41.4 ​% of BRAF-negative and 44.8 ​% of RET/PTC-negative patients.

[CONCLUSION] Molecular testing in nodules ≥4 ​cm may underestimate malignancy risk. Clinicians should interpret benign MT results in this subgroup with caution.