PD-1 Antibody for The Prevention of Adenomatous Polyps and Second Primary Tumors in Lynch Syndrome Patients

Inclusion Criteria:

1. Lynch syndrome with germline variants of MLH1, MSH2, or EPCAM (pathogenic or likely pathogenic variants)
2. Necessary treatments have been done, such as surgery, chemotherapy, radiation therapy, etc.
3. Have a resection, including right hemicolectomy, left hemicolectomy, sigmoid colectomy, or anterior resection of rectal cancer, or endoscopic adenoma resection
4. Aged 18-70 years old
5. Eastern Cooperative Oncology Group (ECOG) performance score of 0 to 1
6. White blood cell (WBC) \> 4000/mm3, Platelet count \>100000/mm3, HB \>10 g/dL
7. Serum glutamic-oxaloacetic transaminase (SGOT) \< 1.5 × the upper limit of normal (ULN), Serum glutamic pyruvic transaminase (SGPT) \< 1.5 × ULN prior to randomization, Total bilirubin (TBIL) \< 1.5 mg/dL
8. Serum creatinine (Scr) \<1.8 mg/dL

Exclusion Criteria:

1. Lynch syndrome with germline variants of MSH6 and PMS2
2. Previous immunotherapy has been taken, such as anti-PD-1, anti-PD-L1, etc.
3. Long-term use of aspirin
4. Suffering from autoimmune diseases
5. Active infection with hepatitis B or hepatitis C (high copy number of viral DNA) or human immunodeficiency virus (HIV)
6. Other clinically serious active infections (NCI-CTC 4.0)
7. With cachexia or organ dysfunction
8. Suffering from seizures requiring treatment (such as steroids or antiepileptic therapy)
9. Unable to participate or complete the study due to substance abuse, or medical, psychological, or social disorder
10. Known allergy to any drugs in this study
11. Pregnant or nursing women, or women of childbearing potential who are not using adequate contraception
12. Any unstable condition or situation that could compromise the safety and compliance of participants.
13. Failure to sign an informed consent form