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Postoperative Management of Differentiated Thyroid Cancer
Goals of Postoperative Management
Differentiated thyroid cancer (DTC) is being diagnosed with increasing incidence, but the mortality rate has remained low. The vast majority of these tumors are low-risk cancers, limited to the thyroid gland, which have a 20-year disease-specific survival rate close to 100%. Current recommendations aim to best adapt adjuvant therapy and follow-up to each patient and each cancer, avoiding overtreatment and oversurveillance of indolent disease while escalating therapy for cancers with a high risk of recurrence and/or death. Current treatment paradigms will avoid unnecessary acute toxicity and long-term side effects associated with radioactive iodine (RAI) and thyroid hormone replacement therapy while effectively diagnosing and treating patients with distant metastases (DM) with appropriate techniques and drugs, improving quality of life and progression-free survival. Current classifications divide patients into risk groups that determine the extent of recommended adjuvant therapy and follow-up.
Treatment According to Risk of Cancer Recurrence
Certain clinical, preoperative, and postoperative histopathological tumor and patient characteristics enable physicians to evaluate risk factors for recurrence and classify patients into groups according to the estimated risk of tumor recurrence. Table 47.1 enumerates these characteristics for each risk group, according to the American Thyroid Association (ATA) Guidelines published in 2015.
Table 47.1
Risk Grouping According to the American Thyroid Association Guidelines
| ATA Risk Group | Tumor Characteristics | Estimated Risk of Recurrence |
|---|---|---|
| Low-risk papillary carcinoma | Intrathyroidal micropapillary carcinoma (single or multifocal, including BRAFV600E mutated) or Papillary carcinoma with all of the following characteristics: No local or distant metastases All macroscopic tumor has been resected No tumor invasion of locoregional tissues or structures No aggressive histology No vascular invasion Clinical N0 or N1 with ≤ 5 micrometastases all < 2 mm in largest dimension No RAI-avid metastatic foci outside the thyroid bed on the first posttreatment whole-body RAI scan (if 131 I is given) |
≤ 5% |
| Low-risk follicular carcinoma | Intrathyroidal, well-differentiated follicular thyroid carcinioma with capsular invasion and < 4 foci of vascular invasion | |
| Intermediate risk | Papillary of follicular cancer with any of the following: Microscopic invasion of perithyroid soft tissues Aggressive histology Papillary thyroid cancer with vascular invasion Clinical N1 or > 5 N1 all < 3 cm in the largest dimension RAI-avid metastatic foci in the neck outside the thyroid bed on the first posttreatment whole-body RAI scan |
5%–20% |
| High risk | Papillary of follicular cancer with any of the following: Macroscopic invasion of perithyroid soft tissues and/or structures N1 with any metastatic node > or = 3 cm in the largest dimension Incomplete tumor resection Distant metastases Follicular cancer with extensive vascular invasion (> 4 foci) Postoperative serum thyroglobulin suggestive of distant metastases |
> 20% |
RAI, radioactive iodine; 131 I, iodine-131.
The American Joint Commission on Cancer classification evaluates the risk of death from thyroid cancer, which is based on the extent of disease, tumor size, location of regional lymph node metastases, and the presence of DM. The stage grouping according to age illustrated the excellent outcomes of treatment for patients < 55 years old, even with DM, compared with older patients ( Boxes 47.1 and 47.2 ).
Box 47.1
TNM Classification
T—Primary Tumor
T1a: intrathyroidal tumor ≤ 1 cm
(m) multifocal tumor
T1b: intrathyroidal tumor > 1cm but ≤ 2 cm
T2: intrathyroidal tumor > 2 cm but < 4 cm
T3a: intrathyroidal tumor > or = 4 cm
T3b: tumor of any size with gross extrathyroidal extension invading strap muscles
T4a: extrathyroidal extension with invasion of any of the following: subcutaneous soft tissues, larynx, trachea, esophagus, recurrent laryngeal nerve
T4b: tumor invades prevertebral fascia or mediastinal vessels or encases carotid artery
N—Regional Lymph Nodes
Nx: regional lymph nodes cannot be assessed
N0a: no regional lymph node metastasis on cytology or pathology of at least one lymph node
N0b: no regional lymph node metastases on palpation and ultrasound
N1a: metastases to the central compartment (level VI) and/or upper mediastinal lymph nodes (level VII)
N1b: metastases in other unilateral, bilateral, or contralateral cervical lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph node
M—Distant Metastases
M0: no distant metastases
M1: distant metastases
Box 47.2
TNM Stage Grouping
In clinical practice, the indications for adjuvant treatment after surgery are currently based on the risk grouping as described in the ATA guidelines. For epidemiologic purposes and prognostication, the tumor, node, metastases (TNM) classification is employed.
Adjuvant treatments include RAI, external beam radiation therapy (EBRT), thyroid hormone replacement or suppression therapy, localized treatment of individual metastatic lesions, and systemic therapies mainly with orally administered tyrosine kinase inhibitors (TKIs).
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