The staging of thyroid cancer is a critical factor in determining the appropriate treatment plan. Based on the degree of cancer spread, the stages are defined as follows:

Stage 1: The tumor is confined solely within the thyroid gland and has not spread to other tissues or organs.
Stage 2: The cancer has begun to spread outside the thyroid gland to nearby surrounding tissues.
Stage 3: Cancer cells have spread to the lymph nodes around the thyroid gland and to adjacent tissues in the neck.
Stage 4: The cancer has metastasized to distant organs such as the lungs or bones.