Immune Checkpoint Inhibitors for Organ Preservation in Non-metastatic dMMR/MSI-H Gastric or Colon Cancers

Inclusion Criteria: * Subjects are able to comprehend the informed consent form, and voluntarily sign the informed consent form. * Subjects are ≥18 years old on the day of signing the informed consent form, with no gender restrictions. * Histologically confirmed gastric cancer or colon cancer, without distant metastasis based on CR or MR. * ECOG performance status of 0-2. * dMMR confirmed by immunohistochemistry or MSI-H confirmed by PCR and NGS. If MSI status and MMR status were not consistent, whether to enroll this patient should be determine by investigators. Patients with MMR heterogeneity in tumors could not be included. * Patients who are about to receive or are receiving 24 weeks of PD1/PDL1 antibody monothearpy and have not had the first efficacy assessment. * Archived tumor tissue samples or freshly obtained tumor tissue samples are available. * Female subjects of childbearing potential or male subjects with partners of childbearing potential agree to use highly effective contraception from 7 days before the first dose until 120 days after the last dose. Female subjects of childbearing potential must have a negative serum pregnancy test within 7 days before the first dose. * Subjects have the ability and willingness to comply with the study protocol's visits, treatment plan, laboratory tests, and other study-related procedures. * For patients who are about to receive combination of Sintilimab, IBI310 and Lenvatinib. subjects should have good organ function within t…