Thyroid cancer, like most others, is staged based upon three criteria:
T = how large the main tumor is when it is found
N = the presence of cancer in lymph nodes and their location
M = whether the cancer has spread or metastasized to other parts of the body. Thyroid cancer has been known to spread locally or to distant parts of the body including lungs and bone.
Staging from I to IV, including subgroups, is different for each type of cancer and helps predict outcome and survival. There are also different staging considerations for patients older or younger than age 45 for papillary and follicular thyroid cancers.