['colorectal cancer']
['atezolizumab (mpdl3280a), an engineered anti-pdl1 antibody', 'cobimetinib', 'regorafenib']

        Inclusion Criteria:

        Disease-specific inclusion criteria:

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

          -  Experienced disease progression or was intolerant to at least two systemic
             chemotherapy regimens for metastatic colorectal cancer that must have included
             fluroropyrimidines, irinotecan, and oxaliplatin; adjuvant regimen can be considered as
             one chemotherapy regimen for metastatic disease if the participant had disease
             recurrence within 6 months of completion; disease progression must have occurred
             within 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 of
             contraception (failure rate of less than [<] 1 percent [%] per year) during the
             treatment period, within 5 months after the last dose of atezolizumab, and within 3
             months after the last dose of cobimetinib and regorafenib

          -  Men must agree not to donate sperm or have intercourse with a female partner without
             using appropriate barrier contraception during the treatment period and for 3 months
             after 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-mutant
             participants will be eligible

          -  Major surgery or radiotherapy within 21 days prior to Cycle 1 Day 1 or anticipation of
             needing 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 must
             be on a stable regimen at study entry

          -  Uncontrolled pleural effusion, pericardial effusion or ascites requiring repeated
             drainage 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 the
             past 3 years are excluded. Participants with completely resected cutaneous melanoma
             (early stage), basal cell carcinoma, cutaneous squamous cell carcinoma, cervical
             carcinoma in-situ, breast carcinoma in-situ, and localized prostate cancer are
             eligible

          -  Unstable angina, new onset angina within last 3 months, myocardial infarction within
             last 6 months and current congestive heart failure New York Heart Association Class II
             or higher

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

          -  Poorly controlled hypertension, defined as a blood pressure consistently above 150/90
             millimeters 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 is
             considered a risk factor for central serous retinopathy, retinal vein occlusion, or
             neovascular macular degeneration

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

          -  History of autoimmune disease

          -  History of idiopathic pulmonary fibrosis, organizing pneumonia, bronchiolitis
             obliterans, 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 administered
             medications

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

          -  Administration of a live, attenuated vaccine within 4 weeks before randomization or
             anticipation of a live attenuated vaccine will be required during the study
      