Study of Bevacizumab + mFOLFOX6 Versus Bevacizumab + FOLFIRI With Biomarker Stratification in Participants With Previously Untreated Metastatic Colorectal Cancer (mCRC)

Inclusion Criteria:

* Histologically or cytologically confirmed colorectal cancer (CRC) with at least one measurable metastatic lesion by RECIST Version 1.1
* Archival tumor tissue sample must be requested and available prior to study entry. If no archival tumor tissue sample is available, a fresh biopsy tissue sample must be obtained but should be discussed first with the medical monitor. A copy of the local pathology report must be submitted along with the specimens.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
* Participants with treated brain metastases are eligible for study participation. Participants may not receive ongoing treatment with steroids at Screening. Anticonvulsants (at stable dose) are allowed. Treatment for brain metastases may be whole-brain radiotherapy, radiosurgery, neurosurgery, or a combination as deemed appropriate by the treating physician. Radiotherapy and stereotactic radiosurgery must be completed at least 28 days prior to randomization.
* Female participants should not be pregnant or breastfeeding. Female participants with childbearing potential should agree to use effective, non-hormonal means of contraception during the study and for a period of at least 6 months following the last administration of study drugs. Female participants with an intact uterus (unless amenorrheic for the last 24 months) must have a negative serum pregnancy test within 7 days prior to randomization into the study.
* Male participants must agree to use effective contraception during the study and for a period of at least 6 months following the last administration of study drugs, even if they have been surgically sterilized.

Exclusion Criteria:

* Any prior systemic treatment for mCRC
* Adjuvant chemotherapy for CRC completed \<12 months
* Evidence of Gilbert's syndrome or of homozygosity for the UGT1A1\*28 allele
* Known positivity for human immunodeficiency virus (HIV)
* Malignancies other than mCRC within 5 years prior to randomization, except for adequately treated carcinoma in situ of the cervix, basal or squamous cell skin cancer, localized prostate cancer treated surgically with curative intent, and ductal carcinoma in situ treated surgically with curative intent
* Radiotherapy to any site for any reason within 28 days prior to randomization, except for palliative radiotherapy to bone lesions within 14 days prior to randomization
* Clinically detectable third-space fluid collections that cannot be controlled by drainage or other procedures prior to study entry
* Treatment with any other investigational agent, or participation in another investigational drug trial within 28 days prior to randomization