To explore the efficacy and safety of radiotherapy followed by PD-1+ standard chemotherapy in the first-line treatment of initial unresectable rectal cancer liver metastases

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.