The malignant manifestation of thyroid nodules is thyroid cancer. Thus, thyroid nodules are divided into two major categories: benign and malignant. Benign nodules generally make up the vast majority, with malignancies accounting for less than 5%. Malignant thyroid nodules are cancerous. Some benign thyroid nodules may also become malignant over time. Generally, small nodules do not show obvious clinical symptoms during the cancerous transformation, but their nature changes. When a nodule compresses surrounding tissues and causes certain symptoms, such as hoarseness, tracheal compression, and difficulty swallowing, it often indicates that the tumor is in the middle or late stage. Overall, the chances of benign nodules becoming cancerous are very small. The malignancy rate of benign nodular goiter is about 5%, and the possibility of adenomas turning malignant is around 10%. As the diameter increases, the possibility of adenomas becoming malignant gradually increases. There are several high-risk factors for the malignant transformation of thyroid nodules: for instance, having a history of radiation exposure to the head and neck area during childhood or adolescence, patients who are younger than 14 or older than 70; the rate of malignant transformation of thyroid nodules significantly increases; and the rate of malignant transformation in male nodules is significantly higher than in females. Also, patients whose nodules significantly increase in size in a short period during regular check-ups are also considered high-risk for malignancy.