The precursors of cancerous thyroid nodules can be judged from thyroid ultrasound, clinical manifestations and treatment effects, such as thyroid ultrasound showing changes of blood flow in the nodules. 1. Thyroid ultrasound: if the size and shape of thyroid nodules change, such as obvious enlargement within a short period of time, irregular edges, change of blood flow in the nodules, enlargement of lymph nodes around the thyroid nodules, etc., we should suspect the risk of cancerous transformation of thyroid nodules. 2. Clinical manifestations: when patients with thyroid nodules have difficulty in swallowing, hoarseness, dyspnea, after excluding respiratory diseases and esophageal diseases, they should be alerted to the cancerous change of thyroid nodules. 3. Treatment effect: If thyroid nodules do not decrease but increase after treatment, consider the possibility of thyroid nodule cancer. For patients considering thyroid nodule cancer, thyroid ultrasonography, thyroid function review, fine needle aspiration biopsy and, if necessary, surgical excision should be performed under the guidance of physicians.