Thyroid 4c is a grading under ultrasound of thyroid nodule, which indicates a high possibility of malignant changes, and it is recommended to seek prompt medical attention to improve further examination and treatment. Thyroid nodules can be classified into grades 1 to 6 according to their color ultrasound imaging, i.e., whether the blood flow signal is abundant or not, whether the aspect ratio of the thyroid nodule is more than one, and whether the thyroid nodule is accompanied by calcification, and according to the grading to initially assess its malignant potential. Generally, below grade 3, the probability of malignant disease is less than 2%, and the probability of malignancy in grade 4 is more than 2%. grade 5 is highly suspected of thyroid malignancy; and grade 6 is a patient with thyroid cancer who has been detected by puncture cytology, and after microscopic examination, thyroid cancer cells have been detected. And in the middle of thyroid grade 4, there are grades 4a, 4b and 4c. For thyroid nodule grade 4c, the probability of malignancy is 50% to 90%. In other words, with a grade 4c thyroid nodule, there is more than a 50% chance that it is a malignant tumor, which is thyroid cancer. Once there is a judgment like this one, the patient is expected to go to a regular hospital immediately for further diagnosis and treatment. Although thyroid 4c is highly suspicious of thyroid malignancy, there is no need to be overly nervous, and it is sufficient to seek timely medical attention and follow the doctor’s instructions for examination and treatment.