The "T" stage is as follows:

• T1-tumor 1 cm or less within the thyroid gland
• T2-tumor sized 1-4 cm within the thyroid gland
• T3-tumor size greater than 4 cm within the thyroid gland
• T4-tumor of any size extending outside of the thyroid gland itself

The "N" stage is as follows:

• N0-no spread to lymph nodes
• N1-tumor spread to lymph nodes
• N1a-spread to lymph nodes on the same side of the neck as the primary tumor
• N1b-spread to lymph nodes bilaterally or to the opposite side of the primary tumor

The "M" stage is as follows:

• M0-no tumor spread to other organs
• M1-tumor spread to other organs

The overall stage is based on a combination of these T, N, and M parameters as well as age (to emphasize the fact that younger patients have a better prognosis) and type of thyroid cancer (to emphasize that papillary and follicular thyroid cancers have excellent prognoses while anaplastic thyroid cancers have poor prognoses).

• Papillary or Follicular Thyroid Cancer, age > 45 years
• Stage I-T1, N0, M0
• Stage II-T2-3, N0, M0
• Stage III-T4, N0, M0 or any N1, M0
• Stage IV-any M1

• Papillary or Follicular Thyroid Cancer, age <45 years
• Stage I-any M0
• Stage II-any M1

• Medullary Thyroid Cancer, any age
• Stage I-T1, N0, M0
• Stage II-T2, N0, M0
• Stage III-any N1, M0
• Stage IV-any M1

• Anaplastic Thyroid Cancer, any age
• ALL designated as Stage IV to denote the aggressiveness of anaplastic thyroid cancer