The study evaluates the combination of immunotherapy of PD-1 antibody and neoadjuvant short-course radiotherapy in early low rectal cancer. A total of 34 patients will receive 5*5Gy short-course radiotherapy, followed by 4 cycles of capecitabine plus oxaliplatin (CAPOX) chemotherapy and PD-1 antibody, finally receive the local excision(TEM) or total mesorectal excision (TME). The rate of complete response (cCR+pCR), Organ retention rate, long-term prognosis, and adverse effects will be analyzed.

Inclusion Criteria:

1. age 18-70 years old, female and male
2. pathological confirmed adenocarcinoma
3. clinical stage T1-3bN0, tumor maximum diameter less than 4cm
4. the distance from anal verge less than 5 cm
5. without distance metastases
6. KPS >=70
7. with good compliance
8. microsatellite repair status is MSS/pMMR
9. without previous anti-cancer therapy or immunotherapy
10. signed the inform consent

Exclusion Criteria:

1. pregnancy or breast-feeding women
2. pathological confirmed signet ring cell carcinoma
3. clinical stage T1N0 and can be resected locally
4. history of other malignancies within 5 years
5. serious medical illness, such as severe mental disorders, cardiac disease, uncontrolled infection, etc.
6. immunodeficiency disease or long-term using of immunosuppressive agents
7. baseline blood and biochemical indicators do not meet the following criteria: neutrophils≥1.5×10^9/L, Hb≥90g/L, PLT≥100×10^9/L, ALT/AST ≤2.5 ULN, Cr≤ 1 ULN
8. DPD deficiency
9. allergic to any component of the therapy

Individual participant data that underlie the results reported in the related article, after deidentification (text, tables, figures, and appendices).

Beginning 3 months and ending 5 years following related article publication.

Proposals should be directed to xxx@yyy. To gain access, data requestors will need to sign a data access agreement. Data are available for 5 years at a third party website (Link will to be included).