Thyroid cancer is typically a primary cancer located within the thyroid gland, according to the American Cancer Society. Thyroid cancer can then spread out from the thyroid gland into lymph nodes in the neck, behind the throat and in the upper chest.
The stage of a thyroid tumor is determined by its size, the extent to which cancer cells have spread to nearby lymph nodes and the extent to which cancer has metastasized to other parts of the body, notes the American Cancer Society. When thyroid cancer spreads from the primary tumor, it most often metastasizes to the bones, liver and lungs. While the stage of most thyroid tumors is expressed on a scale from 0 to 4, anaplastic thyroid tumors begin at stage 4.