Welcome from Priyathama Vellanki, MD
Thyroid nodules are common in the adult population. With the use of increased imaging, more thyroid nodules are incidentally discovered. Accordingly, the incidence of thyroid cancer has increased. Despite the increased incidence of thyroid cancer, mortality from thyroid cancer remains low and has not changed despite increased detection.1 Therefore, an important aspect in clinical care is to determine which thyroid nodules warrant a biopsy and those that can be safely followed.
The American Thyroid Association (ATA) published guidelines in 2006 and 2009 to address the management of thyroid nodules.2 Since 2009, there have been many retrospective and prospective studies that have added to the current guidelines.
Fine-Needle Aspiration, Ultrasound
While fine-needle aspiration (FNA) remains the gold standard for evaluation of thyroid nodules and to rule out malignancy. However, with the advent of more sensitive ultrasound (US) imaging, more studies have been conducted correlating US features with malignancy in order to reduce unnecessary biopsies. All nodules that undergo FNA are classified into one of the 6 categories of the Bethesda classification system.3 The 6 categories correlate to different malignancy risk.
Most Thyroid Nodules are Benign
Most thyroid nodules in adults are reported as benign. Current guidelines recommend that benign nodules should be followed using serial US exams.2 However, retrospective studies have shown this may not be necessary and benign nodules usually stay benign. The findings from retrospective studies have been confirmed prospectively by Durante and colleagues.4 While the study by Durante et al had only 5 years of follow-up, it demonstrated that most benign nodules do not grow, and nodule growth is not necessarily a marker of malignant transformation.
Follow-up of an indeterminate nodule as categorized by the Bethesda system of atypia of uncertain significance/follicular lesion of uncertain significance (AUS/FLUS), follicular neoplasm (FN), and suspicious for malignancy (SMC) is difficult for both the clinician and the patient. AUS/FLUS, FN and SMC comprise 9.7%, 10.1% and 2.7% respectively of all thyroid FNAs.5 Since the risk for malignancy is higher for the indeterminate nodules compared to benign nodules, usually the recommendation is to repeat FNA or perform diagnostic lobectomy. However, this may result in unnecessary fine-needle aspirations and surgeries.
Commercially available molecular marker tests have been validated for aiding the clinical management of thyroid nodules that fall into the indeterminate category by the Bethesa reporting system.3 Depending on the particular molecular test and the pretest probability of malignancy, molecular tests can aid the clinician's evaluation as to whether the indeterminate nodule is likely to be malignant or benign. The ATA also published guidelines for the use of molecular testing in 2015, which will be further discussed.
Overall, there are multiple studies that can help improve the clinician's management of thyroid nodules. In this EndoScan, we will discuss some of the newer guidelines and studies that have impacted the management of thyroid nodules.
1. Ahn HS, Kim HJ, Welch HG. Korea's thyroid-cancer "epidemic"--screening and overdiagnosis. N Engl J Med. 2014;371:1765-1767.
2. Cooper DS, Doherty GM, Haugen BR, Kloos RT, et al. American Thyroid Association Guidelines Taskforce on Thyroid Nodules and Differentiated Thyroid Cancer. Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2009;19:1167-1214.
3. Cibas ES, Ali SZ. The Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2009;19:1159-1165.
4. Durante C, Costante G, Lucisano G, Bruno R, et al. The natural history of benign thyroid nodules. JAMA. 2015;313:926-935.
5. Bongiovanni M, Spitale A, Faquin WC, Mazzucchelli L, Baloch ZW. The Bethesda System for Reporting Thyroid Cytopathology: a meta-analysis. Acta Cytologica. 2012;56:333-339.