A Study to Investigate Efficacy and Safety of Cobimetinib Plus Atezolizumab and Atezolizumab Monotherapy Versus Regorafenib in Participants With Metastatic Colorectal Adenocarcinoma (COTEZO IMblaze370)

Inclusion Criteria: Disease-specific inclusion criteria:

• Histologically confirmed adenocarcinoma originating from the colon or rectum (Stage 4American Joint Committee on Cancer [AJCC] 7th edition)

• Experienced disease progression or was intolerant to at least two systemicchemotherapy regimens for metastatic colorectal cancer that must have includedfluroropyrimidines, irinotecan, and oxaliplatin; adjuvant regimen can be considered asone chemotherapy regimen for metastatic disease if the participant had diseaserecurrence within 6 months of completion; disease progression must have occurredwithin 3 months of the last systemic therapy administration General inclusion criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

• Anticipated life expectancy greater than or equal to (>=) 3 months

• Adequate hematologic and end organ function

• Women of childbearing potential must agree to appropriately use an effective form ofcontraception (failure rate of less than [<] 1 percent [%] per year) during thetreatment period, within 5 months after the last dose of atezolizumab, and within 3months after the last dose of cobimetinib and regorafenib

• Men must agree not to donate sperm or have intercourse with a female partner withoutusing appropriate barrier contraception during the treatment period and for 3 monthsafter the last dose of either cobimetinib or regorafenib

• Provide an archival or newly obtained tumor tissue sample

Exclusion Criteria:

• After the approximate 5% cap for microsatellite (MSI)-high participants is reached,only MSI-stable participants will be eligible

• Once the 50% cap for wild-type RAS has been reached, only extended RAS-mutantparticipants will be eligible

• Major surgery or radiotherapy within 21 days prior to Cycle 1 Day 1 or anticipation ofneeding such procedure while receiving study treatment

• Treatment with any anti-cancer agent within 14 days prior to Cycle 1 Day 1

• Uncontrolled tumor-related pain. Participants requiring narcotic pain medication mustbe on a stable regimen at study entry

• Uncontrolled pleural effusion, pericardial effusion or ascites requiring repeateddrainage more than once every 28 days. Indwelling drainage catheters (e.g., PleurX®)are allowed

• Active or untreated central nervous system (CNS) metastases are excluded

• Prior therapy with any cancer immunotherapy, MEK inhibitor, or regorafenib

• Participants with active malignancy (other than CRC) or a prior malignancy within thepast 3 years are excluded. Participants with completely resected cutaneous melanoma (early stage), basal cell carcinoma, cutaneous squamous cell carcinoma, cervicalcarcinoma in-situ, breast carcinoma in-situ, and localized prostate cancer areeligible

• Unstable angina, new onset angina within last 3 months, myocardial infarction withinlast 6 months and current congestive heart failure New York Heart Association Class IIor higher

• Left ventricular ejection fraction (LVEF) below institutional lower limit of normal orbelow 50%, whichever is lower

• Poorly controlled hypertension, defined as a blood pressure consistently above 150/90millimeters of Mercury (mmHg) despite optimal medical management

• Human immunodeficiency virus (HIV) infection

• Active tuberculosis infection

• Severe infections within 2 weeks prior to Cycle 1 Day 1

• Active or chronic viral hepatitis B or C infection

• History of or evidence of retinal pathology on ophthalmologic examination that isconsidered a risk factor for central serous retinopathy, retinal vein occlusion, orneovascular macular degeneration

• Participants will be excluded if they currently have any of the risk factors asdefined in the study protocol for retinal vein occlusion

• History of autoimmune disease

• History of idiopathic pulmonary fibrosis, organizing pneumonia, bronchiolitisobliterans, drug-induced pneumonitis, or idiopathic pneumonitis

• History of organ transplantation including allogeneic bone marrow transplantation

• Inability to swallow medications

• Malabsorption condition that would alter the absorption of orally administeredmedications

• Pregnant, lactating, breastfeeding, or intending to become pregnant during the study

• Administration of a live, attenuated vaccine within 4 weeks before randomization oranticipation of a live attenuated vaccine will be required during the study