Is it true that a drop of blood can determine if you have cancer? This has always been the desire of people to have a less tedious test. Nowadays, the pollution of food and environment has increased the incidence of cancer year by year, and currently, one out of every four deaths is caused by cancer. That is why there is a great deal of attention to detect cancer by blood drop. I believe many people have measured tumor markers through blood tests during medical checkups. Although there are many kinds of tumor markers, unfortunately none of them can directly confirm the diagnosis, let alone directly see cancer cells. Therefore, blood drop to know cancer has almost become a gimmick. Recognition changed in 2009 when the FDA approved a method for detecting circulating tumor cells in the blood for clinical use. The detection of circulating tumor cells lies in the fact that the tumor cells in blood can be directly separated out and directly observed under a microscope, thus the accuracy of this examination technique approaches the current gold standard of tumor diagnosis: pathological examination. Nowadays, circulating tumor cell test can be applied to the screening of high-risk people in medical examination and also to the treatment of cancer patients. It is just that this test is not much promoted and not well known due to its slightly expensive price. It has been widely used in Europe and America because the cost is not an issue. Currently, the Department of Medical Oncology of Tongji Hospital is also carrying out this examination technique. Therefore, in terms of blood sampling can be checked to determine whether one has cancer or not, blood drop to know cancer can really be done.