• Signed Informed Consent Form

• Age ≥18 years at time of signing Informed Consent Form

• Ability to comply with the study protocol

• MSS or pMMR tumor determined by local CLIA-certified PCR or IHC testing respectively.

• Histologically or cytologically confirmed resectable non-metastatic adenocarcinoma of the colon.

• The distal extent of the tumor must be ≥12 cm from the anal verge on pre-surgical endoscopy and/or imaging (i.e., excluding rectal adenocarcinomas warranting treatment with chemoradiation). If the patient did not undergo a pre-surgical endoscopy, then the distal extent of the tumor must be ≥12 cm from the anal verge as determined by surgical examination or pre-operative imaging.

• One or more of the following high-risk features:

‣ High CEA levels (\>5 ng/ml in non-smoker patients , \>10ng/ml in smoker patients)

⁃ Low Lymphocyte-to-monocyte Ratio (\<2.38)

⁃ Poor grade of tumor differentiation

⁃ Evidence of Lymphovascular Invasion

⁃ Evidence of Perineural Invasion

⁃ CT evidence of T3 orT4 disease w/ ≥4 cm tumor longitudinal diameter

⁃ CT evidence of regional lymphadenopathy

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-1

• Adequate hematologic and end-organ function, defined by the following laboratory test results, obtained within 14 days prior to initiation of study treatment:

‣ ANC ≥ 1.5 x 10\*9/L (1500/mL) without granulocyte colony-stimulating factor support

⁃ Lymphocyte count ≥ 0.5 x 10\*9/L (500/µL)

⁃ Platelet count ≥100 x 10\*9/L (100,000/µL) without transfusion

⁃ Hemoglobin ≥ 9 g/L (9 g/dL) Patients may be transfused to meet this criterion.

⁃ AST, ALT, and alkaline phosphatase (ALP) ≤ 2.5 x upper limit of normal (ULN)

⁃ Serum bilirubin ≤ 1.5 x ULN with the following exception:

∙ Patients with known Gilbert disease: serum bilirubin ≤ 3 x ULN

• Serum creatinine ≤1.5 x ULN or Creatinine clearance ≥ 50 mL/min (calculated using the Cockcroft-Gault formula)

• Serum albumin ≥ 25 g/L (2.5 g/dL)

• For patients not receiving therapeutic anticoagulation: INR or aPTT ≤ 1.5 x ULN

‣ For patients receiving therapeutic anticoagulation: stable anticoagulant regimen

⁃ Negative hepatitis B surface antigen (HBsAg) test at screening

⁃ Negative hepatitis C virus (HCV) antibody test at screening, or positive HCV antibody test followed by a negative HCV RNA test at screening The HCV RNA test must be performed for patients who have a positive HCV antibody test.

⁃ Negative HIV test at screening

⁃ For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods, and agreement to refrain from donating eggs, as defined below:

∙ Women must remain abstinent or use contraceptive methods with a failure rate of \< 1% per year during the treatment period and for 5 months after the final dose of atezolizumab and for 6 months following any of the adjuvant chemotherapy regimens (if applicable) after the final dose of mFOLFOX6 or CAPEOX.Women must refrain from donating eggs during this same period.

∙ A woman is considered to be of childbearing potential if she is postmenarchal, has not reached a postmenopausal state (≥ 12 continuous months of amenorrhea with no identified cause other than menopause), and has not undergone surgical sterilization (removal of ovaries, fallopian tubes and/or uterus) or another cause as determined by the investigator (e.g., Müllerian agenesis). Per this definition, a woman with a tubal ligation is considered to be of childbearing potential. The definition of childbearing potential may be adapted for alignment with local guidelines or requirements.

∙ Examples of contraceptive methods with a failure rate of \< 1% per year include bilateral tubal ligation, male sterilization, hormonal contraceptives that inhibit ovulation, hormone-releasing intrauterine devices, and copper intrauterine devices.

∙ The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or postovulation methods) and withdrawal are not adequate methods of contraception. If required per local guidelines or regulations, locally recognized adequate methods of contraception and information about the reliability of abstinence will be described in the local Informed Consent Form.

∙ • For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm, as defined below: With a female partner of childbearing potential who is not pregnant, men who are not surgically sterile must remain abstinent or use a condom plus an additional contraceptive method that together result in a failure rate of \<1% per year during the treatment period and for 5 months after the final dose of any chemotherapy regimen. Men must refrain from donating sperm during this same period.

∙ With a pregnant female partner, men must remain abstinent or use a condom during the treatment period and for 5 months after any of the chemotherapy regimens to avoid exposing the embryo.

∙ The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or postovulation methods) and withdrawal are not adequate methods of contraception. If required per local guidelines or regulations, locally recognized adequate methods of contraception and information about the reliability of abstinence will be described in the local Informed Consent Form.