• Histologically proven diagnosis of colorectal cancer;

• Initially unresectable metastatic colorectal cancer not previously treated with chemotherapy for metastatic disease;

• Proficient mismatch repair (pMMR) status in tumour tissue (primary or metastatic), as determined by a local laboratory assay in a CLIA- or similarly certified;

• Immunoscore IC-high status in tumour tissue (primary or metastatic), as determined by a sponsor-defined central laboratory (HEGP, AP-HP, INSERM, France).

• At least one measurable lesion according to RECIST criteria (version 1.1);

• Availability of adequate tumour specimen (primary or metastatic);

• Male or female of 18-75 years of age;

• ECOG PS ≤ 2 if aged \< 71 years, ECOG PS = 0 if aged 71-75 years;

• Life expectancy of at least 12 weeks;

• Previous adjuvant chemotherapy allowed only if with fluoropyrimidine monotherapy and more than 6 months elapsed between the end of adjuvant and first relapse;

• Neutrophils \>1.5 x 109/L, Platelets \>100 x 109/L, Hb \>9 g/dl;

• Total bilirubin ≤1.5 times the upper-normal limits (UNL) of the normal values and AST (SGOT) and/or ALT (SGPT) \<2.5 x UNL (or \<5 x UNL in case of liver metastases) alkaline phosphatase \<2.5 x UNL (or \<5 x UNL in case of liver metastases);

• Creatinine clearance ≥50 mL/min or serum creatinine ≤1.5 x UNL;

• INR or aPTT ≤1.5 x ULN. This applies only to patients who are not receiving therapeutic anticoagulation;

• Urine dipstick of proteinuria \<2+. Patients discovered to have 2+ proteinuria on dipstick urinalysis at baseline, should undergo a 24-hour urine collection and must demonstrate ≤1 g of protein/24 h;

• Women of childbearing potential must have a negative blood pregnancy test at the baseline visit. For this trial, women of childbearing potential are defined as all women following menarche and until becoming post-menopausal unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high follicle stimulating hormone (FSH) level in the postmenopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. However, in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient;

• Male subjects with female partners of childbearing potential and female subjects of childbearing potential must, therefore, be willing to use adequate contraception as approved by the investigator (barrier contraceptive measure or oral contraception) and outlined in Section 6.5 - Contraception, starting with the first dose of study therapy through 6 months after the last dose of bevacizumab and fluorouracil and within 5 months after the last dose of atezolizumab.

• Females of childbearing potential must have a negative blood pregnancy test at the baseline visit (i.e., performed maximum 7 days before the treatment start);

• Will and ability to comply with the protocol;

• Written informed consent to study procedures.