Thyroid cancer on the left side may metastasize to lymph nodes on the right side and other sites. Thyroid cancer is the most common thyroid malignant tumor, which can be classified into papillary carcinoma, follicular adenocarcinoma, medullary carcinoma and undifferentiated carcinoma according to the pathological types, and all the four types of thyroid cancers can have lymph node metastasis. Thyroid cancer on the left side is likely to metastasize to the right side and other parts of the lymph nodes. The most common manifestation of thyroid cancer is a mass found in the thyroid gland. If localized lymph node metastasis occurs, enlargement of lymph nodes in the neck can occur, and in some patients, enlargement of lymph nodes in the neck is the first manifestation. Advanced cancer cells can also metastasize to lungs, bones and other organs. Treatments for thyroid cancer include surgery, radionuclide (iodine 131) therapy, TSH suppression therapy and external radiation therapy. If you feel unwell, please consult a doctor promptly.