The number of patients requiring clinical evaluation of thyroid nodules has dramatically increased over the past three decades due to the increasing number of thyroid incidentalomas [1
]. Fine-needle aspiration (FNA) biopsy is the most accurate and cost-effective preoperative test to distinguish benign from malignant thyroid nodules. Most thyroid nodules are benign and only about 5% of them have malignant features on FNA biopsy and cytologic examination. Unfortunately, FNA biopsy is inconclusive in about 30% of all thyroid nodule biopsies because the cytologic features are indeterminate (follicular and Hürthle neoplasm), suspicious for malignancy but not completely diagnostic, or nondiagnostic (insufficient cells) upon cytologic examination. These patients are typically subjected to a diagnostic thyroidectomy to exclude a thyroid cancer diagnosis. Approximately 20% of patients with FNA biopsy showing indeterminate cytologic features will have thyroid cancer on histologic examination and may require a completion thyroidectomy.
Although FNA biopsy is accurate for benign and malignant interpretations, up to 10% of benign cytologic results may be false negatives and result in delay in diagnosis and treatment [2
]. Also, significant discordance in the thyroid FNA biopsy cytologic interpretation has been reported on secondary review, especially for indeterminate, nondiagnostic, and suspicious findings [3
]. The discordance in thyroid FNA biopsy interpretation can have significant management ramifications, ranging from patients avoiding thyroidectomy to allowing for more definitive initial surgical treatment in some cases. In order to decrease the need for unnecessary procedures and the additional costs incurred for diagnostic and completion thyroidectomies, new approaches to improving the diagnostic accuracy of FNA biopsy are needed.
Thyroid cancer marker research has been an active area with numerous approaches and candidate markers emerging but very few markers have been evaluated in a clinical trial to find whether they would be useful in clinical practice [4
]. Molecular testing for common somatic mutations is one promising approach that has emerged because about two-thirds of thyroid cancers of follicular cell origin have one of the common genetic alterations (BRAF and RAS point mutations and RET/PTC and NTRK1 rearrangements), the genetic changes that occur are usually mutually exclusive events, and most of these genetic changes are specific to thyroid cancer of follicular cell origin (BRAF mutation and RET/PTC rearrangements). Somatic genetic alterations in thyroid cancer of follicular cell origin occur in genes involved in the tyrosine kinase signaling pathway (tyrosine kinase receptors: RET/PTC and NTRK1; intracellular signaling proteins: HRAS, KRAS, NRAS, and BRAF). The most prevalent genetic alteration is a point mutation in BRAF (V600E), which is present in approximately 40% of classic papillary thyroid cancers. RET/PTC and NTRK1 chromosomal rearrangements are present in about 30% and up to 15% of classic papillary thyroid cancers, respectively [4
]. Hotspot mutations in NRAS and KRAS are more common in follicular thyroid carcinoma but also occur in benign thyroid neoplasm at a lower rate.
Several studies have reported that testing for the common somatic genetic changes in thyroid cancer may be useful for detecting thyroid cancer in indeterminate and suspicious thyroid FNA biopsy results [5
]. Most of these studies were retrospective, tested for a limited number of genetic changes, and/or had a relatively small group of indeterminate, suspicious, and nondiagnostic FNA cytology groups. In fact, at the National Cancer Institute State of the Science Conference on thyroid FNA biopsy, it was suggested that although promising, there was limited data to recommend molecular testing for common somatic genetic alterations as an ancillary test to thyroid FNA biopsy for indeterminate and suspicious cytologic findings [16
In this prospective clinical trial, we wanted to determine the feasibility and accuracy of molecular testing for a comprehensive panel of somatic genetic alterations associated with thyroid cancer of follicular cell origin in clinical thyroid FNA biopsy samples. We evaluated 455 thyroid nodule FNA biopsy samples from 417 patients using PCR and direct sequencing for hotspot mutations in BRAF, NRAS, and KRAS, and nested PCR for RET/PTC1, RET/PTC3, and NTRK1 rearrangements.