A Clinical Study of Calderasib (MK-1084) With Targeted Therapy and Chemotherapy in People With Colorectal Cancer (MK-1084-012/KANDLELIT-012)

Researchers are looking for other ways to treat locally advanced or metastatic colorectal cancer (mCRC) that is unresectable and has a gene mutation called KRAS G12C. Standard (or usual) treatments for this type of colorectal cancer may include mFOLFOX6 with or without bevacizumab. Researchers want to learn if adding calderasib (the study medicine) and cetuximab to mFOLFOX6 can treat locally advanced or mCRC with the KRAS G12C mutation. Calderasib and cetuximab are targeted therapies. The goals of this study are to learn: * About the safety of calderasib with cetuximab and mFOLFOX6 and if people tolerate the treatments * If people who receive calderasib with cetuximab and mFOLFOX6 live longer without mCRC growing or spreading compared to people who receive mFOLFOX6 with or without bevacizumab.

This study will have 2 parts.

Inclusion Criteria: The main inclusion criteria include but are not limited to the following: * Has a histologically confirmed diagnosis of locally advanced unresectable or metastatic (unresectable Stage III or Stage IV as defined by American Joint Committee on Cancer \[AJCC\] eighth edition) colorectal adenocarcinoma * Part 2 only: Has not received systemic anticancer therapy for locally advanced unresectable or metastatic colorectal cancer * Tumor tissue demonstrates presence of a Kirsten rat sarcoma viral oncogene homolog G12C (KRAS G12C) mutation * Human immunodeficiency virus (HIV)-infected participants must have well controlled HIV on antiretroviral therapy (ART) * Participants who are Hepatitis B surface antigen (HBsAg) positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy and have undetectable HBV viral load * Participants with history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable Exclusion Criteria: The main exclusion criteria include but are not limited to the following: * Has active inflammatory bowel disease requiring immunosuppressive medication or previous clear history of inflammatory bowel disease (eg, Crohn's disease, ulcerative colitis, chronic diarrhea) * Has uncontrolled, significant cardiovascular disease or cerebrovascular disease * Has known dihydropyrimidine dehydrogenase (DPD) deficiency * HIV-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease * Has received prior systemic anticancer therapy including investigational agents within 4 weeks before randomization * Has 1 or more conditions that, in the opinion of the investigator, make the participant ineligible for treatment with bevacizumab * Has known additional malignancy that is progressing or has required active treatment within the past 3 years * Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis or leptomeningeal disease * Has active infection requiring systemic therapy * Has not adequately recovered from major surgery or have ongoing surgical complications * Has a history of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease