A prognosis is a prediction of the outcome of one’s disease. How likely is survival? Will the cancer come back? These are the big questions on most people’s minds after receiving a diagnosis of well-differentiated thyroid cancer. In general, there are several characteristics of the tumor that can inform a patient about their chances of being cured.
Factors That Affect Prognosis
Stage
This is the most important factor that affects a patient’s chance of being cured.
Site
The location and size of the tumor in the thyroid gland can affect the surgeon’s ability to resect the tumor with adequate margins of healthy tissue around it.
Type and Grade
Both the type and grade of the tumor determine the amount of treatment necessary and the ultimate prognosis.
Spread to Lymph Nodes
This helps determine stage, but even without other factors, spread to lymph nodes in the neck decreases the chance of cure, especially if there is evidence of growth of cancer outside of the lymph node. Both the number and size of lymph nodes are also important, as a low number of small lymph nodes may not increase a patient’s risk significantly.
Age
A patient’s age at diagnosis is a significant factor in determining stage. Patients younger than 55 years old can only be Stage I or II.
While each of these factors contributes to one’s outcome, patients should have a discussion with their doctor to determine their overall prognosis. Giving a percentage of survival is challenging because cancer research often looks at multiple types of cancer and may include a large range of patients who underwent a variety of treatments.
Although the TNM staging system is intended to define the risk of mortality associated with thyroid cancer, the American Thyroid Association (ATA) has developed a system that is intended to determine the risk of developing recurrent thyroid cancer. The chance of recurrence should be reevaluated at each follow-up visit after primary treatment. Perhaps contrary to what one might think, recurrent cancer can often be successfully treated and does not always lead to a higher risk of dying from disease.
The most recent (2015) American Thyroid Association (ATA) Guidelines for papillary and follicular thyroid cancer identify the following factors which indicate low, intermediate, or high-risk disease.
Low Risk Factors
- Cancer limited to the thyroid gland.
- ≤5 lymph node micrometastases (<0.2 cm in size) (small spread of tumor into lymph nodes).
Intermediate Risk Factors
- Aggressive histology (microscopic changes in the tumor that indicate aggression).
- Minimal extension of tumor outside the thyroid gland.
- Vascular invasion (spread of tumor into blood vessels).
- >5 involved lymph nodes (0.2-3.0 cm in size).
High Risk Factors
- Gross extension of tumor outside the thyroid gland.
- Incomplete tumor resection.
- Distant metastases (spread of thyroid cancer to another part of the body).
- Lymph node metastasis >3cm in size.
Prognosis of Papillary & Follicular Thyroid Cancer
SEER stands for Surveillance, Epidemiology, and End Results Program. The SEER database is a large American cancer database that tracks 5-year relative survival rates for cancer in the United States, based on how far the cancer has spread. Instead of grouping cancers according to AJCC TNM stages (I,II,III,IV), SEER categorizes cancers into localized, regional, and distant stages.
Survival Rates for Patients with Papillary Thyroid Cancer
| SEER Stage | Estimated Disease-Specific Survival at 5 Years |
| Localized | 99.9% |
| Regional | 99.9% |
| Distant | 78% |
Survival Rates for Patients with Follicular Thyroid Cancer
| SEER Stage | Estimated Disease-Specific Survival at 5 Years |
| Localized | 99.9% |
| Regional | 96% |
| Distant | 56% |
- Localized: There is no sign that the cancer has spread outside of the thyroid.
- Regional: The cancer has spread outside of the thyroid to nearby structures.
- Distant: The cancer has spread to distant parts of the body such as the bones.
Disclaimer: Estimated Disease-Specific Survival is the percentage of people with a specific cancer who are alive at a given time point, such as five years after diagnosis. It excludes people who may have died from a disease other than their cancer. While these estimates from large national databases are helpful, it is important to remember that these broad statistics may not apply to one’s individual situation. The information above is provided according to SEER data.
