Stable microsatellites in colon cancer indicate that immunotherapy is not effective. Microsatellites are short tandem repetitive sequences found throughout the human genome and are present in large numbers. Because errors can easily occur during replication, they are relatively stable if the body’s normal mismatch repair system can correct replication errors. Immunotherapy is a new method of treating malignant tumors, with relatively good therapeutic effect and small side effects, but it is not suitable for all malignant tumor patients. If colon cancer microsatellite is not stable, immunotherapy can be taken, but the specific treatment effect needs to be analyzed comprehensively according to the actual situation. For colon cancer patients with stable microsatellites, the prognosis is relatively poor and not suitable for immunotherapy. Doctors need to determine the appropriate treatment plan after evaluation.