Thyroid cancer: Stage and prognosis

What is the staging system?

The extent, or stage of cancer, is used to determine the prognosis (i.e. the chance that a patient will recover, have a recurrence, or die of a disease) and the best treatment plan for an individual. The stage of thyroid cancer is determined by the size of the largest tumor in the thyroid gland, whether it is confined to the thyroid gland, or if it has spread to other parts of the body (lymph nodes and distant sites). The most common thyroid cancer staging system used is the TNMTNM - most common thyroid cancer staging system; Tumor size, lymph Node status, distant Metastasis (Tumor size, lymph Node status, distant Metastasis). The different parts of the TNM staging system are:

Tumor size:

TX: Primary tumor cannot be assessed
T0: No evidence of primary tumor
T1: 2 cm or smaller
T2: 2 to 4 cm
T3: > 4 cm or has grown a small amount just outside the thyroid
T4a: Any size tumor that has grown beyond the thyroid gland into nearby tissues of the neck
T4b: Any size that has grown back toward the spine or into nearby large blood vessels

Lymph nodes:

NX: Regional (nearby) lymph nodes cannot be assessed
N0: No spread to nearby lymph nodes
N1: Spread to nearby lymph nodes
N1a: Spread to lymph nodes next to the thyroid (central neck)
N1b: Spread to lymph nodes in the sides of the neck (lateral neck) or to the lymph nodes in the upper chest (mediastinal)

Distant metastasis:

MX: Presence of distant metastasis (spread) cannot be assessed
M0: No distant metastasis
M1: Distant metastasis is present, involving distant lymph nodes, internal organs, bones

Lower stages (i.e. I or II vs. III or IV) have a better overall prognosis for both survival and lower disease recurrence rates. The most important factor in staging thyroid cancer (papillary, follicular and Hurthle cell) is the patient's age. Patients who are younger than 45 years old at the time of diagnosis are a stage I no matter how large the tumor is or whether or not there are positive lymph nodes. If they are younger than 45 years old at the time of diagnosis and the cancer has spread to distant sites (i.e. metastasis), such as lungs, bones, or other organs, then they are considered stage II.

Patients older than 45 years at the time of diagnosis with papillary, follicular, and Hurthle cell thyroid cancers and all patients with medullary thyroid cancer, are staged as described below:

Stage I (T1, N0, M0): <2 cm across, with no spread to lymph nodes or distant sites.

Stage II (T2, N0, M0): 2 to 4 cm across, with no spread to lymph nodes or distant sites.

Stage III (T3, N0, M0 or T1 to T3, N1a, M0)

The tumor is larger than 4 cm or has grown slightly outside the thyroid, but it has not spread to nearby lymph nodes or distant sites.
The tumor is any size and has spread to lymph nodes around the thyroid in the neck (cervical nodes) but not to distant sites.

Stage IVA (T4a, N0 to N1a, M0 or T1 to T4T4 - thyroxine thyroid hormone, N1b, M0): One of the following applies:

The tumor is any size and has grown beyond the thyroid gland to invade nearby tissues of the neck. It may or may not have spread to lymph nodes around the thyroid in the neck (central neck). It has not spread to distant sites.
The tumor is any size and may have grown outside the thyroid gland. It has spread to lymph nodes in the side of the neck (lateral neck) or upper chest (mediastinal) but not to distant sites.

Stage IVB (T4b, any N, M0): The tumor is any size and has grown either into the spine or into nearby large blood vessels. It may or may not have spread to nearby lymph nodes, but it has not spread to distant sites.

Stage IVC (any T, any N, M1): The tumor is any size and may or may not have grown outside the thyroid. It may or may not have spread to nearby lymph nodes, but it has spread to distant sites.

In addition to the TNM staging system there have been other staging systems used which also accurately predict the risk of tumor recurrence and prognosis for thyroid cancer. Nonetheless, TNM staging is used by the World Health Organization (WHO) and is most commonly used in the U.S.