Retrograde dissemination of cancer cells is one of the main symptoms of colorectal cancer tumor infiltration and metastasis, colorectal cancer is the general term of colon cancer and rectal cancer, colorectal cancer is a malignant lesion of colorectal mucosal epithelium occurring under the action of various carcinogenic factors such as environment or genetics, etc. The prognosis is poor and the mortality rate is high. Colorectal cancer is a malignant tumor of colorectal mucosal epithelial origin. It is one of the most common malignant tumors of the gastrointestinal tract. Examination of retrograde dissemination of cancer cells caused by colorectal cancer: 1. Laboratory examination Laboratory examinations such as blood routine, biochemical full (liver and kidney function + serum iron), stool routine + stool occult blood, etc. can help to understand whether the patient has iron deficiency anemia, liver and kidney function and other basic conditions. Blood tumor marker carcinoembryonic antigen (CEA) test is performed to help the diagnosis of tumor. In patients with colorectal cancer, high CEA level does not mean that all of them have distant metastasis; there are a few patients with metastases, CEA is not increased. 2.Endoscopy Colonoscopy is to extend a fiberoptic colonoscope into the ileocecal region at the beginning of the colon to examine the colon and rectal cavity, and to perform biopsy and treatment during the examination. Colonoscopy is more accurate than barium enema X-rays, especially for small colon polyps, which are removed by colonoscopy and confirmed pathologically. Removal of benign polyps can prevent their transformation into colorectal cancer, and cancerous polyps can help clarify the diagnosis and treatment. Biopsy and exfoliative cytology examination Biopsy is decisive for confirming the diagnosis of colorectal cancer, especially early stage cancer and polyp cancer, and for differential diagnosis of lesions, which can clarify the nature, histological type and malignancy of tumor, judge the prognosis and guide clinical treatment. The accuracy of abscission cytology examination is high, and it is not easy to obtain satisfactory specimens, so it has little clinical application.