Thyroid nodules are common, and while most are benign, evaluating their cancer risk is crucial, involving ultrasound, biopsy, and sometimes advanced tests to guide management decisions.

Thyroid nodules are lumps or growths that form within the thyroid gland, a butterfly-shaped gland located at the base of your neck. These nodules are quite common, with many people developing them at some point in their lives. The vast majority of thyroid nodules are benign (non-cancerous) and do not cause any symptoms. However, a small percentage can be malignant (cancerous), making accurate evaluation of their cancer risk a critical step in patient care [2].

Initial Evaluation: Ultrasound and Biopsy

The first step in evaluating a thyroid nodule typically involves an ultrasound. This imaging technique helps characterize the nodule's size, shape, borders, and internal features, which can provide clues about its potential nature. Systems like the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) or the British Thyroid Association's 'U' classification (ultrasound reporting system) categorize nodules based on these ultrasound features to stratify malignancy risk [3, 6]. For instance, a 'U3' classification indicates an indeterminate nodule with a 35.4% chance of malignancy [6].

If ultrasound findings suggest a higher risk, a fine-needle aspiration biopsy (FNAB) is often performed. During an FNAB, a thin needle is used to collect cells from the nodule, which are then examined under a microscope. The results are commonly classified using the Bethesda System for Reporting Thyroid Cytopathology. Nodules categorized as Bethesda III or IV are considered 'indeterminate,' meaning the cells don't clearly indicate whether the nodule is benign or malignant [2, 5].

In some cases, a core needle biopsy (CNB) might be used, especially for certain indeterminate nodules or even low-suspicion nodules (K-TIRADS category 3) if specific risk factors are present. One study found that 36.5% of resected low-suspicion nodules were malignant, with a well-defined halo and hypervascularity identified as independent risk factors for malignancy in these cases [8].

Navigating Indeterminate Nodules

Indeterminate thyroid nodules (Bethesda III and IV) present a significant diagnostic challenge. These nodules carry an intermediate risk of malignancy, and deciding between active surveillance or diagnostic surgery can be complex [5]. Studies show that among patients who undergo surgery for Bethesda III or IV nodules, approximately one-third are ultimately found to be malignant upon histopathological examination [5]. For example, one study found that 52 out of 181 patients had cytologically indeterminate nodules, highlighting the need for accurate preoperative diagnosis to guide surgical strategy [2].

Specific Conditions and Risk Factors

Certain medical conditions and personal histories can increase the risk of thyroid cancer in the presence of nodules:

Graves' Disease (GD): This autoimmune disorder is frequently associated with thyroid nodules. A retrospective analysis found that among GD patients with nodules who underwent thyroidectomy, 26.2% had thyroid carcinoma confirmed by histopathology [1]. This emphasizes the importance of careful evaluation for malignancy in GD patients with thyroid nodules [1].
Familial Adenomatous Polyposis (FAP): Patients with FAP have a significantly increased risk of developing thyroid nodular disease and thyroid cancer. Screening thyroid ultrasounds can detect nodules in 30% of FAP patients at initial screening, and 14% of those with a normal baseline ultrasound developed new nodules over a median follow-up of 7 years [4]. This group requires refined surveillance recommendations [4].
Clinical Risk Factors: A positive family history of thyroid cancer, a history of radiation exposure to the head and neck, and a documented growth in the size or number of nodules are all considered clinical risk factors that increase the suspicion of malignancy [2].

Advanced Tools for Risk Assessment

To improve the accuracy of preoperative diagnosis, especially for indeterminate nodules, several advanced tools are being explored:

Molecular Testing: This involves analyzing nodule cells for specific genetic mutations or variants associated with thyroid cancer, such as the BRAF V600E mutation [2, 7]. Molecular tests can help refine the risk assessment for indeterminate nodules, guiding treatment decisions [2, 7].
Ki-67 Labeling Index: This is a marker of cell proliferation. Digitally quantifying the Ki-67 labeling index in core needle biopsy specimens, either alone or combined with ultrasound risk stratification systems like K-TIRADS, has shown potential in predicting malignancy, particularly in category IV nodules [3].
Nomograms: Researchers are developing nomograms, which are predictive models that integrate multiple risk factors. One such nomogram combines the BRAF V600E mutation status, serum biomarkers, and ultrasound features to provide an individualized malignancy risk estimate for C-TIRADS 3 and 4 nodules, especially when cytology results are unclear [7].
Combined Ultrasound Scores: Combining different ultrasound risk stratification scores, such as the 'U' score with a 'Thy' score, can enhance risk prediction. For instance, a U3, Thy-3f nodule was associated with a 38% malignancy rate in one study [6].

When is Surgery Considered?

The ultimate goal of thyroid nodule evaluation is to accurately establish a preoperative diagnosis to determine the most appropriate management, including the extent of surgery if needed [2]. For indeterminate nodules, the decision to proceed with surgery is often based on a comprehensive assessment of all available information, including clinical risk factors, ultrasound features, biopsy results, and advanced molecular or biomarker testing [2, 5]. Approximately one-third of indeterminate nodules undergoing surgery are found to be malignant, underscoring the importance of these diagnostic pathways [5].

Sources

[1] Increased Risk of Thyroid Cancer in Patients with Graves' Disease and Thyroid Nodules: A Retrospective Analysis. https://pubmed.ncbi.nlm.nih.gov/42510122/
[2] Clinical and molecular genetic analysis of cytologically uncertain thyroid nodules in patients with thyroid disease. https://pubmed.ncbi.nlm.nih.gov/38058193/
[3] Integrating Digital Ki-67 Labeling Index and K-TIRADS for Malignancy Risk Stratification in Thyroid Core Needle Biopsies. https://pubmed.ncbi.nlm.nih.gov/42512325/
[4] Progression of Nodular Thyroid Disease in Familial Adenomatous Polyposis Syndrome: Refined Surveillance Recommendations. https://pubmed.ncbi.nlm.nih.gov/38782203/
[5] Prevalence and predictors of malignancy in Bethesda III and IV thyroid nodules undergoing surgery. https://pubmed.ncbi.nlm.nih.gov/42676365/
[6] Can we better advise our patients with nodular thyroid disease? https://pubmed.ncbi.nlm.nih.gov/37185056/
[7] Nomogram integrating BRAF V600E, serum biomarkers, and ultrasound features for malignancy risk stratification in C-TIRADS category 3 and 4 thyroid nodules. https://pubmed.ncbi.nlm.nih.gov/42724081/
[8] Indications for Core Needle Biopsy in Low-Suspicion Thyroid Nodules on US. https://pubmed.ncbi.nlm.nih.gov/42568825/

This article summarises published research for a general audience. It is not medical advice — talk to a qualified clinician about your own situation. Need help finding one? Browse doctors.