From the Guidelines
The likelihood of metastasis in thyroid cancer varies significantly depending on the type of thyroid cancer and individual risk factors, with papillary thyroid cancer having a relatively low metastasis rate of about 5-20%, primarily spreading to regional lymph nodes, as indicated in the 2019 ESMO clinical practice guidelines for diagnosis, treatment, and follow-up of thyroid cancer 1.
Risk Factors for Metastasis
The risk of metastasis in thyroid cancer is influenced by several factors, including:
- Type of thyroid cancer: Papillary, follicular, medullary, and anaplastic thyroid cancers have different metastasis rates, with anaplastic thyroid cancer being the most aggressive 1.
- Tumor size: Larger tumors, especially those greater than 4cm, have a higher risk of metastasis 1.
- Genetic mutations: Certain genetic mutations, such as BRAF V600E, can increase the risk of metastasis 1.
- Extension beyond the thyroid capsule: Tumors that extend beyond the thyroid capsule have a higher risk of metastasis 1.
- Vascular invasion: Tumors with vascular invasion have a higher risk of metastasis 1.
Monitoring and Detection of Metastasis
Regular monitoring through:
- Ultrasound
- Thyroglobulin blood tests
- Occasional whole-body scans is essential for early detection of metastasis, as indicated in the 2019 ACR Appropriateness Criteria for thyroid disease 1 and the 2018 NCCN Guidelines for Thyroid Carcinoma 1.
Prognosis
The overall prognosis remains excellent for most thyroid cancers, with 5-year survival rates exceeding 95% for papillary and follicular types, even with limited regional metastasis, as indicated in the 2018 NCCN Guidelines for Thyroid Carcinoma 1.
From the FDA Drug Label
Metastases were present in 99% of the patients: lungs in 89%, lymph nodes in 52%, bone in 39%, liver in 18%, and brain in 4% The likelihood of metastasis of thyroid cancer is high, with metastases present in 99% of patients, most commonly in the:
- Lungs (89%)
- Lymph nodes (52%)
- Bone (39%)
- Liver (18%)
- Brain (4%) 2
From the Research
Likelihood of Metastasis in Thyroid Cancer
The likelihood of metastasis in thyroid cancer is a complex topic that has been studied extensively.
- The most common sites of locoregional metastases associated with thyroid cancer are the cervical lymph nodes (LNs) in the central (level VI) and lateral (levels II-V) compartments of the neck 3.
- Distant metastasis is reported in 1.22% of patients with thyroid cancer, with the distribution of metastatic cases varying based on pathology and tumor size 4.
- Significant predictors of distant metastasis include older age, male gender, non-White minorities, presence of multiple comorbidities, minimal gross extrathyroidal extension (ETE), lymphovascular invasion (LVI), and concomitant central and lateral lymph node metastasis (LNM) 4.
Risk Factors for Metastasis
Several risk factors have been identified as increasing the likelihood of metastasis in thyroid cancer.
- Tumor size and pathology are important factors, with larger tumors and certain types of thyroid cancer (such as follicular thyroid carcinoma) being more likely to metastasize 4.
- The presence of lymph node metastasis, ETE, and LVI also increase the risk of distant metastasis 4.
- The number and size of lymph nodes, as well as the presence of extranodal extension (ENE), impact risk stratification 5.
Diagnosis and Management
Diagnosis and management of metastatic thyroid cancer are critical for improving patient outcomes.
- Preoperative assessment of lymph nodes can be done using cervical ultrasound (US) or contrast-enhanced computed tomography (CT) of the neck 3.
- Postoperative surveillance after total thyroidectomy can be done using US, CT, and biochemical data such as thyroglobulin (Tg) levels 3.
- The prognosis for patients with metastatic thyroid cancer is generally poor, but a subset of patients with oligometastasis can be managed surgically and may have a better outcome 6.