Clinically, thyroid cancer is classified as stage T1 if the tumor is less than 2 cm in diameter; stage T2 if the tumor is 2-4 cm in diameter and confined to the thyroid gland; stage T3 if the tumor is larger than 4 cm in diameter or has broken through the envelope and invaded the anterior cervical tissues; stage T4 if the tumor breaks through the thyroid gland and encircles other structures of the neck, such as blood vessels and nerves. Depending on the stage and course of the disease, thyroid cancer stage T1 is the early stage of cancer, while stage T4 is the advanced stage of cancer. The corresponding treatment for different stages is not the same, but thyroid cancer generally has a better prognosis.