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Staging is the process used by doctors to determine the extent of spread of cancer in the body. Staging is important because it helps doctors to develop an individualized treatment plan and is also useful for predicting the outcome (prognosis).

The classification system used for staging patients with thyroid cancer is known as the TNM classification system which consists of the following three components:

• T = Tumor Size - refers to the size of the tumor
• N = Lymph Nodes - indicates whether or not the cancer has spread to any nearby (regional) lymph nodes
• M = Metastasis - indicates whether or not the cancer has spread to distant organs such as the lungs, bones, or brain.

Each of the three components of the TNM system is assigned a numerical score and the scores are then combined to determine the stage of the disease. Patients are assigned to one of four stage groupings designated by Roman numerals I through IV. In general, the higher the stage grouping the more extensive the spread of the cancer in the body.

Stage Groupings for Differentiated Thyroid Cancer

A key feature of the TNM classification system for differentiated thyroid cancer (papillary and follicular carcinoma) is that it makes a distinction between younger patients (under age 45) and older patients (over age 45). This age distinction is based on the observation that younger patients under age 45 with differentiated thyroid cancer have a higher survival rate than patients over age 45.

Staging of Younger Patients Under Age 45

The TNM classification system groups patients under age 45 into either Stage I or Stage II based solely upon the presence or absence of metastasis (M score) of the cancer to distant sites. Irrespective of the size of the tumor (T score) or regional lymph node involvement (N score), patients younger than age 45 are assigned to Stage I if the cancer has not spread to distant sites. If the cancer has spread to distant sites (e.g., lungs, bones, brain), patients are assigned to Stage II.

This same staging system is used to group patients with medullary thyroid carcinoma (MTC).

Staging for Older Patients Over Age 45

Patients over age 45 with differentiated thyroid cancer are staged by the TNM classification system into one of the following four major groups:

• Stage I - This is the earliest stage of the disease where the tumor is confined to the thyroid gland and is small in size (less than 2.0 cm).

• Stage II - The tumor is still confined to the thyroid gland but is larger in size (2.0 to 4.0 cm) than in Stage I.

• Stage III - This is a more advanced stage of thyroid cancer and includes either:

  • Large tumors (greater than 4.0 cm) that are confined to the thyroid gland; OR

  • Tumors of any size that have invaded regional lymph nodes but have not spread to distant sites.

• Stage IV - This is the most advanced stage of differentiated thyroid cancer and is further subdivided into the following subgroups:

  • Stage IVA - Includes any tumor has spread beyond the thyroid gland to nearby tissues; to regional lymph nodes; or to lymph nodes in the upper mediastinum (upper chest area). At this stage, the tumor has not spread to distant sites.