PROGNOSIS
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 tumour 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 tumour in the thyroid gland can affect the surgeon’s ability to resect the tumour with adequate margins of healthy tissue around it.

Type and Grade

Both the type and grade of the tumour 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.

Low Risk Factors

  • Cancer limited to the thyroid gland.
  • ≤5 lymph node micrometastases (<0.2 cm in size) (small spread of tumour into lymph nodes).

Intermediate Risk Factors

  • Aggressive histology (microscopic changes in the tumour that indicate aggression).
  • Minimal extension of tumour outside the thyroid gland.
  • Vascular invasion (spread of tumour into blood vessels).
  • >5 involved lymph nodes (0.2-3.0 cm in size).

High Risk Factors

  • Gross extension of tumour outside the thyroid gland.
  • Incomplete tumour resection.
  • Distant metastases (spread of thyroid cancer to another part of the body).
  • Lymph node metastasis >3cm in size.