Cystic masses are usually not malignant. Cystic changes can only occur on top of benign masses, benign nodules, so they are described as cystic masses under ultrasound. If the mass is malignant, it is filled with tumor cells, it is a solid nodule, and the tumor cells are growing very vigorously, so there will be no cystic changes. Only when the tumor cells have impaired blood supply, necrosis and hemorrhage may occur on the surface of the tumor. Take thyroid nodules as an example, nodular goiter and thyroid adenoma are common benign diseases, especially nodular goiter, which may become cystic and may even bleed inside the cystic lesion, so it may manifest as a sudden enlargement of the thyroid gland and the patient may have some pain. Ultrasound examination can clarify the diagnosis, and once the diagnosis is clear, surgery is usually required.