Safety and Efficacy of PD-1 ± mFOLFOX6 Neoadjuvant Therapy in Local Advanced sMPCC

Inclusion Criteria:

1. Histological confirmation of simultaneous multiple primary colorectal cancer (sMPCC);
2. Tumor biopsy immunohistochemistry of at least one tumor lesion identified dMMR, including the expression loss of one or more of the four proteins MSH1, MSH2, MSH6 and PMS2; or at least one tumor lesion identified MSI-H by polymerase chain reaction or next-generation sequencing technique;
3. Clinical staging T3-4NxM0, with or without positive MRF, with or without positive EMVI;
4. Staging method: all patients undergo chest,abdominal and pelvic enhanced CT, rectal palpation, high resolution MRI examination，positive perienteric lymph node(LN): short diameter ≥10mm LN or LN with typical metastatic shape and MRI character, clinical data should be re-evaluated and judged by center evaluation group when there are contradictory stagings，distant metastasis were excluded by chest and abdominal enhanced CT and pelvic enhanced MRI;
5. No intestinal obstruction symptom，or obstruction relieved after proximal colostomy;
6. No colorectal surgery history;
7. No chemotherapy or radiotherapy history;
8. No biopharmaceutical treatment history(such as monoclonal antibody), immunotherapy(such as anti PD-1antibody, anti PD-L1 antibody, anti PD-L2 antibody or anti CTLA-4), or other research drug treatment;
9. No endocrinotherapy history restriction;
10. informed consent assigned.

Exclusion Criteria:

1. Arrhythmia need anti-arrhythmia treatment(except β-blocking agent or Digoxin), symptomatic coronary heart disease or myocardial ischemia(myocardial infarction within 6 months) or congestive heart-failure (CHF) \> NYHA grade II;
2. Severe hypertension not well controlled by drugs;
3. HIV infection history or active phase of chronic Hepatitis B or C(high copies of virus DNA);
4. Active tuberculosis(TB), accepting anti-TB treatment or anti-TB treatment within 1 year before trial screen;
5. Other active clinical severe infection(NCI-CTC AE V5.0);
6. Outside pelvic distant metastasis evidences;
7. Dyscrasia, organ dysfunction;
8. Pelvic or abdominal radiotherapy history;
9. Epilepsy need treatments(Steroid or anti-epilepsy therapy);
10. Other malignant tumor history within 5 years;
11. Over abuse of drugs, medical and psychological or social conditions that might interfere patients or evaluation of the study results;
12. Any active autoimmune disease or autoimmune disease history (including but not restricted: interstitial pneumonia, uveitis, enteritis, hepatitis, hypophysitis, nephritis, hyperthyroidism, hypothyroidism, asthma need bronchodilators);
13. Any anti-infection vaccine injection 4 weeks before inclusion;
14. Long-term exposure to immune-suppressor, combination of systemic or topical use of corticosteroids (dose\>10mg/day prednisolone or equivalent hormone);
15. Known or suspicious allergy to any study related drugs;
16. Any unstable state might cause damage to the safety and compliance of patients;
17. Pregnant or breast feeding women who has ability to have children while without contraception;
18. Refuse to sign informed consent.