Avelumab Plus 5-FU Based Chemotherapy as Adjuvant Treatment for Stage 3 MSI-High or POLE Mutant Colon Cancer

Inclusion Criteria:

1. Male or female subjects aged ≥18 years
2. ECOG PS 0/1
3. Histologically proven, stage III (i.e., any T, N1 or N2, M0) adenocarcinoma of the colon (as defined by the presence of the inferior pole of the tumour above the peritoneal reflection - that is, at least 15 cm from the anal margin).
4. Fully surgically resected tumour with clear resection margins (i.e., \>1 mm)
5. Locally confirmed defective mismatch repair (dMMR) tumour (as defined by the lack of staining on either the pre-operative biopsy samples or resection specimens of at least one of the following proteins: MLH1 (mutL homolog 1), MSH2 (mutS homologue 2), MSH6 (mutS homolog 6), PMS2 or centrally confirmed POLE exonuclease domain mutated tumour (in subjects \<50 years old with pMMR tumours)
6. Absence of metastases as shown by post-operative CT scan
7. Absence of major post-operative complications or other clinical conditions that, in the opinion of the investigator, would contraindicate adjuvant chemotherapy 8. Adequate hematological function defined by absolute neutrophil count (ANC) ≥1.5 × 109/L, platelet count ≥100 × 109/L, and hemoglobin ≥9 g/dL (blood transfusion before recruitment is allowed)

9\. Adequate hepatic function defined by a total bilirubin level ≤1.5 × the upper limit of normal (ULN) range and AST and ALT levels ≤2.5 × ULN 10. Adequate renal function defined by an estimated creatinine clearance ≥30 mL/min according to the Cockcroft-Gault formula (or local institutional standard method) 11. Negative serum or urine pregnancy test at screening for women of childbearing potential 12. Fertile men and women must agree to take highly effective contraceptive precautions during, and for 6 months after the last dose of chemotherapy or for 1 month after the last dose of Avelumab

Exclusion Criteria:

1. Rectal tumours (as defined by the presence of the inferior pole of the tumour below the peritoneal reflection - that is, \<15 cm from the anal margin).
2. Inability to start adjuvant chemotherapy within 12 weeks after surgery
3. Administration of neoadjuvant systemic chemotherapy or radiotherapy before surgical resection of colon cancer
4. Prior organ transplantation, including allogeneic stem-cell transplantation
5. Significant acute or chronic infections including, among others:

   * known history of testing positive test for human immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome (AIDS)
   * positive test for HBV (Hepatitis B) surface antigen or anti-HCV (Hepatitis C) antibody and confirmatory HCV RNA test
6. Active autoimmune disease that might deteriorate when receiving an immunostimulatory agent:

   * Subjects with diabetes type I, vitiligo, psoriasis, hypo- or hyperthyroid disease not requiring immunosuppressive treatment are eligible
   * Subjects requiring hormone replacement with corticosteroids are eligible if the steroids are administered only for the purpose of hormonal replacement and at doses ≤10 mg/day of prednisone or equivalent
   * Administration of steroids through a route known to result in a minimal systemic exposure (topical, intranasal, intro-ocular, or inhalation) are acceptable
7. Known severe hypersensitivity reactions to monoclonal antibodies (Grade ≥3 NCI-CTCAE v4.0), any history of anaphylaxis, or uncontrolled asthma (that is, 3 or more features of partially controlled asthma)
8. Persisting toxicity related to prior therapy of Grade \>1 NCI-CTCAE v4.0; however, alopecia and sensory neuropathy Grade ≤2 is acceptable unless oxaliplatin administration is planned as part of the adjuvant treatment
9. Pregnancy or lactation
10. Known alcohol or drug abuse
11. Clinically significant (i.e., active) cardiovascular disease: cerebral vascular accident/stroke (\<6 months prior to enrollment), myocardial infarction (\<6 months prior to enrollment), unstable angina, congestive heart failure (≥ New York Heart Association Classification Class II), or serious cardiac arrhythmia requiring medication
12. Known history of colitis, pneumonitis and pulmonary fibrosis (for example, inflammatory bowel disease, uncontrolled asthma), which, in the opinion of the Investigator, might impair the subject's tolerance of trial treatment.
13. Any psychiatric condition that would prohibit the understanding or rendering of informed consent
14. Vaccination within 4 weeks of the first dose of Avelumab and while on trial is prohibited except for administration of inactivated vaccines
15. Other invasive malignancy within 2 years except for non-invasive malignancies such as cervical carcinoma in situ, non-melanomatous carcinoma of the skin or ductal carcinoma in situ of the breast that has/have been surgically cured. Cancer subjects with incidental histological findings of prostate cancer (tumour/node/metastasis stage of T1a or T1b or prostate-specific antigen ˂10) who have not received hormonal treatment may be included, pending a discussion with the study physician.

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