The First-line Treatment of RCLM With RAS Mutation Was Local Short-course Radiotherapy (SCRT) + PD-1+ Standard Therapy

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the rectum； * The clinical stage evaluated by MRI was T3-4 and/or N+ and M1a(only liver metastasis)； * ECOG PS 0-2； * CHild Pugh A； * Estimated survival ≥3 months; * Women of childbearing age should comply with contraceptive measures if pregnancy test is negative; * Adequate organ and bone marrow functions, ecg, blood, biochemical and other basic tests are not contraindications of chemotherapy; * Adherence to scheduled visits, treatment plans, laboratory tests, and other study procedures Willingness and ability. Exclusion Criteria: * Pregnant or lactating women; * No previous antitumor therapy； * No previous liver local therapy； * No contraception during the reproductive period; * patients known to have a history of allergy to any study drug, similar drug or excipient; * Patients with risk of massive gastrointestinal bleeding or gastrointestinal obstruction; * Patients with a history of thromboembolism, except those caused by PICC; * Patients with active infection; * Other conditions that the investigator determines are not suitable for inclusion in the study.