Thyroid Cancer Staging and Initial Treatment Considerations
The American Joint Committee on Cancer (AJCC) and International Union against Cancer (IUCC) developed a pathological staging classification for thyroid tumors (Table 1). The TNM classification provides physicians an abbreviated language useful in describing tumor characteristics.
Table 1. AJCC/UICC TNM Classification System
|Primary Tumor (T Stage)|
|Tx||Primary tumor cannot be assessed|
|T0||No evidence of primary tumor|
|T1a*||Tumor ≤1 cm in greatest dimension, limited to thyroid|
|T1b*||Tumor >1–2 cm in greatest dimension, limited to thyroid|
|T2||Tumor >2 cm and <4 cm in greatest dimension, limited to thyroid|
|T3||Tumor ≥4 cm in greatest dimension, limited to the thyroid or any tumor with minimal extrathyroid extension (eg, extension to sternothyroid muscle or perithyroid soft tissues)|
|T4a||Tumor of any size extending beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve|
|T4b||Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels|
|Regional Lymph Nodes (N Stage)|
|Nx||Regional nodes cannot be assessed|
|N0||No regional lymph node metastasis|
|N1||Regional nodal metastases present|
|N1a||Metastasis to level VI (pretracheal, paratracheal, and prelaryngeal lymph nodes)|
|N1b||Metastasis to unilateral, bilateral, or contralateral cervical or superior mediastinal lymph nodes|
|Distant Metastases (M Stage)|
|Mx||Distant metastases cannot be assessed|
|M0||No distant metastases|
|M1||Distant metastases present|
Used with the permission of the American Joint Committee on Cancer (AJCC), Chicago, Illinois. The original source for this material is the AJCC Cancer Staging Manual, Sixth and Seventh* Editions.
While the AJCC/IUCC classification is useful, it predicts the risk for death, not recurrence.1 The American Thyroid Association (ATA) recommends a three-level classification for risk assessment (Table 2).1
Table 2. ATA Three-level Risk Assessment1
|Low||1. No local or distant metastases|
|2. All the macroscopic tumor has been resected|
|3. No tumor invasion of locoregional tissues or structures|
|4. Tumor does not have aggressive histology|
|5. If 131I is given, there is no 131I uptake outside the thyroid bed on the first post-treatment whole-body Radioactive Iodine (RAI) scan|
|Intermediate||1. Microscopic invasion of tumor into the perithyroidal soft tissues at initial surgery|
|2. Cervical lymph node metastases or 131I uptake outside the thyroid bed on prescribed whole body scan (RxWBS) done after thyroid remnant ablation|
|3. Tumor with aggressive histology or vascular invasion|
|High||1. Macroscopic tumor invasion|
|2. Incomplete tumor resection|
|3. Distant metastases|
|4. Thyroglobulinemia out of proportion to what is seen on the post-treatment scan|
Initial Treatment Considerations for Thyroid Cancer
Differentiated Thyroid Carcinoma
- Total thyroidectomy is generally recommended when the diagnosis of cancer is made pre-operatively. At the time of the thyroidectomy, any involved or suspicious neck lymph nodes are resected.
- Low risk patients do not require further treatment, whereas all other patients would benefit from 131I treatment.
- Suppression of serum TSH by levothyroxine treatment is generally recommended to reduce the risk of recurrence or growth of existent metastases.
- Periodic serum thyroglobulin measurement and neck ultrasonography (ultrasound) are used for long-term surveillance.
- Radioiodine scanning is now performed in patients who are considered at high risk of recurrence or metastatic disease.
- Surgery and/or 131I are used for treatment of recurrent or metastatic disease.
Medullary Thyroid Carcinoma
- When the diagnosis is made pre-operatively, a total thyroidectomy with central compartment dissection is recommended.
- Soon after diagnosis, total thyroidectomy is recommended in patients who carry a genetic mutation. It is recommended soon after birth—when the mutation is known to be aggressive—but this requires a skilled pediatric surgeon. In these patients, it is crucial to screen for pheochromocytoma (adrenal gland tumor) prior to the neck surgery.
- External radiation may have a role in patients with residual disease despite aggressive surgery when there are no significant distant metastases.
- The surgeon should make every effort to preserve speech and swallowing if possible.
- TSH suppression is not needed for these patients, and radioactive iodine has no role.
- Serum calcitonin is used for monitoring.
- The disease is known to metastasize to neck lymph nodes, liver, lungs and skeleton.
- New chemotherapeutic agents may have a role in the control of widely metastatic disease, but no agent is capable of producing complete remission.
Anaplastic Thyroid Carcinoma
Treatment is controversial and disappointing because most cases are clinically advanced when first diagnosed. Surgery may not improve survival. External beam radiation may be helpful for local disease control; however, it does not affect survival, and there is no effective chemotherapeutic regimen.