CTC, also called circulating tumor cell test, is used to detect tumor cells in the peripheral blood circulation. Generally undetectable is the best. If the value detected is less than 2, which means CTC may not be detected or the level of CTC detected is relatively low, this situation is also called normal value. If it is greater than 2 or less than 5, it means that there are tumor cells in the body and there is a possibility of disease progression, but the risk is relatively low. If the value of CTC is above 5, it means that this index is high and the patient may have progressive disease and poor prognosis. However, this circulating tumor cell test should be combined with the patient’s symptoms and imaging examinations, so we cannot judge whether the tumor is developing or not based on this test result alone.