Background: Indeterminate thyroid fine-needle aspiration (FNA) cytology, including atypia of undetermined significance (AUS/FLUS) and suspicious for follicular neoplasm (SFN), continues to generate uncertainty about the presence of malignancy, resulting in repeated follow-up, repeat FNA, or diagnostic surgery. Mutational panel testing may improve the malignancy risk prediction in indeterminate nodules, but the general application of such testing has not been investigated extensively. Methods: A retrospective review was performed of all patients undergoing thyroidectomy at a tertiary care facility over a two-year period. Mutational panel test results, when present, were analyzed relative to FNA cytologic result and surgical histopathologic diagnosis. Malignancy rates, sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV) and positive and negative likelihood ratios (LR) were calculated. Results: A total of 261 operated thyroid nodules had the following initial FNA cytology results: 2% non-diagnostic, 23% benign, 28% AUS/FLUS, 11% SFN, 9% suspicious for malignancy (SUSP), and 27% malignant. The histopathologic malignancy rate was 48%, subcategorized by cytology into benign 7%, AUS/FLUS 30%, SFN 38%, and SUSP 83%. Mutations were more frequent in indeterminate nodules that were histologically malignant versus benign ( p < 0.0001) or versus adenoma ( p = 0.001). Mutational analysis in 44 AUS/FLUS nodules resulted in a malignancy detection sensitivity of 85%, a specificity of 65%, a PPV of 50%, a NPV of 91%, and a positive LR of 2.4. In 12 SFN nodules analyzed with ThyroSeq ^® testing, sensitivity was 100%, specificity 57%, PPV 63%, NPV 100%, and LR 2.3. Performance of the seven-gene mutational panel was not significantly different from the ThyroSeq ^® panel in the AUS/FLUS group. The malignancy yield, comparing the mutation positive AUS/FLUS group with the untested AUS/FLUS surgical cohort, did not reach statistical significance ( p = 0.17). Conclusions: In a surgical cohort, a similar NPV but a lower PPV was found with the use of mutational panel testing compared to the published literature. Following the identification of a mutation, the prevalence of malignancy in the AUS/FLUS or SFN category was increased by nearly 15% to 45% and 53%, respectively. Further study is needed to confirm these results and to analyze clinical outcome subcategories relative to the utility of mutational testing.

Background: Multiple gene mutations in thyroid nodules are rare. The presence of several oncogenic mutations could be associated with aggressive biological behavior of tumors. Patient findings: A 60-year-old female presented to her physician after she felt a lump in her neck. On ultrasound, she was found to have a 1.4 cm × 0.8 cm × 1.3 cm nodule in the isthmus and a 0.5 cm × 0.6 cm ×0.6 cm nodule with irregular margins and hypoechogenicity in the right thyroid lobe, warranting fine-needle aspiration (FNA). Cytological examination of the smaller nodule yielded a diagnosis of atypia of undetermined significance (AUS/FLUS, Bethesda Category III). The aspirate was submitted for molecular testing using the next-generation sequencing ThyroSeq ^® v2 panel. The test revealed four distinct mutations: BRAF (p.V600E), TERT (C228T), PIK3CA (p.H1047R), and AKT1 (p.E17K). Presence of multiple oncogenic mutations in the FNA specimen was highly indicative of cancer, and suggestive of a cancer with propensity toward more aggressive biological behavior. Four weeks after the FNA results were available, the patient underwent total thyroidectomy. This was followed by radioactive iodine ablation after the final pathology revealed a 0.5 cm papillary thyroid carcinoma (PTC) with extrathyroidal extension and positive resection margins (pT3 stage). Summary: Herein, the first case of four mutations preoperatively detected in a subcentimeter thyroid nodule that was confirmed to be a PTC with aggressive biological behavior is reported. Conclusions: The judicious indication of FNA and use of molecular screening can potentially help in predicting aggressive behavior of small-sized thyroid cancers and in identifying patients who may benefit from early and more extensive therapy.