Molecular Testing Can Impact Clinical Decision Making and Therapeutic Approach in Thyroid Cancer

We present the case of a patient with a thyroid nodule of indeterminate cytology on fine-needle aspiration (FNA) biopsy whose molecular profile significantly impacted clinical decision making and treatment. A 77-year-old woman with a history of hyperthyroidism presented to our clinic for a second opinion regarding management of a recently discovered right thyroid nodule. Thyroid ultrasound (US) 6 months prior showed a 2.6 cm, heterogeneous nodule with peripheral vascular flow; not characterized based on ATA or TIRADS criteria. Family history was significant for papillary thyroid cancer in daughter at age 35 years. The patient had no history of head or neck irradiation. She had no compressive symptoms or manifestations of hyper or hypothyroidism. FNA biopsy of the nodule was done twice in 4 months, and cytology was consistent with follicular lesion of undetermined significance (FLUS, Bethesda III) in both occasions. Repeat FNA biopsy at our institution showed follicular neoplasm (FN, Bethesda IV), and molecular testing using ThyroSeq v3 was positive for HRAS and TERT mutations, which conferred a >95% risk of cancer. Patient was referred to Endocrine Surgery and total thyroidectomy was recommended based on nodule’s molecular profile and associated hyperthyroidism. No suspicious lymph nodes were noted on preoperative US. No gross local invasion observed intraoperatively. Surgical pathology showed intrathyroidal FN without invasion. However, given disparity between pathology findings and molecular markers, specimen was sent for outside blinded pathology review which concluded to be a follicular thyroid carcinoma with capsular invasion but no angiolymphatic invasion or extrathyroidal extension. Based on these findings, along with the known HRAS and TERT mutations, it was advised to proceed with radioiodine (RAI) remnant ablation. Patient was prepared with thyrotropin alfa and received 29 millicuries of RAI. Post-treatment scan showed focal neck uptake consistent with ablated thyroid tissue and no distant metastases. Patient had an excellent response to therapy, without evidence of biochemical or structural recurrence 2 years later. Molecular testing of cytologically indeterminate thyroid nodules (Bethesda III, IV) has become an important tool to better refine risk of malignancy. Furthermore, the presence of certain mutations or mutation combinations, such as RAS and TERT co-occurrence, suggests a more aggressive behavior associated with worse outcomes. As a result, a more aggressive approach might be recommended. Our case illustrates how molecular testing can significantly influence therapeutic decisions such as extent of surgery, interpretation of surgical pathology and/or use of RAI. Further research is needed to determine if its routine use may lead to improved cancer-related outcomes or if it is cost-effective in the risk stratification of differentiated thyroid cancer.