Lung metastasis occurs when thyroid cancer is in the advanced stages of cancer because distant metastases such as lungs, liver, etc. can occur in the advanced stages of cancer. The metastasis of thyroid cancer to lungs is usually caused by distant metastasis through lymphatic or blood transportation. Among the thyroid cancers, papillary carcinoma and choriocarcinoma are less malignant and metastasis occurs later, so lung metastasis is less likely to occur at the time of diagnosis; medullary carcinoma is more malignant, and some of them may have already had lung metastasis after the diagnosis; and undifferentiated carcinoma of the thyroid is highly malignant, and lung metastasis is often found after the diagnosis. Thyroid cancer metastasized to the lungs indicates that it has already entered the advanced stage, at this time, it still needs active surgical treatment, and after surgery, it needs to be treated with iodine 131, chemotherapy (such as cisplatin, mitomycin, etc.), in order to remove as many cancer cells as possible.