The separated CTCs were subjected to smear observation, as shown in Fig. 5, in which there was obvious cell morphology under white light, CK19-FITC that identifies the tumor cells was positive, showing green fluorescence, DAPI that identifies the nucleus was positive, showing blue fluorescence, and CD45 used to exclude white blood cells was negative, that is, tumor cells did not show red fluorescence. The gene discussed is KRT19; the disease is neoplasm.