CTC, also known as circulating tumor cells, is used for early diagnosis and prognosis of tumor by detecting fragments of tumor cells remaining in the peripheral blood. Generally, a low value of this index is good, for example, below 2 indicates that no tumor is detected or the tumor is relatively stable, no new development for the time being. If the value is between 2 and 5, the result indicates that there may be progression of the disease, but of course, it should be considered in conjunction with other imaging examinations. If the index of CTC is greater than 5, it means that the cancer cells are more active, and most of them belong to advanced stage patients or highly malignant and aggressive tumors.