Registry Study in MSI/dMMR Solid Tumors

This study plans to enroll patients in the following four cohorts: * Cohort A: Initially only receiving PD1/PDL1 monotherapy; * Cohort B: Initially receiving simultaneous blockade of PD1/PDL1 and CTLA4; * Cohort C: Initially receiving PD1/PDL1 monotherapy combined with chemotherapy or targeted therapy; * Cohort D: Initially not using ICIs, receiving other standard treatments for this tumor type To explore the role of ctDNA testing in therapeutic decision-making, patients with the first evaluation of SD in cohort A are divided into two groups: ctDNA testing/intervention group (Group A1) and ctDNA testing/non-intervention group (Group A2). In group A1, if there is no early response to ctDNA, the researchers and the patient will decide to add CTLA4 antibody or other potentially effective treatments after thorough communication. If there is an early response to ctDNA, then continue with PD1/PDL1 monoclonal antibody treatment. Patients in group A2 undergo ctDNA testing, but still continue with PD1/PDL1 monoclonal antibody treatment according to the RECIST v1.1 standard when the first evaluation of SD is made. Meanwhile, explore the role of 1-year ctDNA-MRD in guiding treatment in patients with long-term tumor control, and explore the guiding role of re-biopsy of tumor tissue or ctDNA testing in helping making treatment regimen after progression on ICIs. Number of Subjects: • This study will recruit patients nationwide for data collection over a period of 3 years. The plan is to enroll 100 cases in Cohort A, including 25 cases in Group A1 and 25 cases in Group A2; 30 cases in Cohort B; 30 cases in Cohort C; and 30 cases in Cohort D.