A Phase 1, Open-label, Multicenter Study to Assess Safety, Tolerability, PK, and Efficacy of MK-1084 as Monotherapy and as Part of Various Combination Therapies in Participants With KRAS G12C Mutant Advanced Solid Tumors

Inclusion Criteria: For all participants: * Has measurable disease by RECIST 1.1 criteria * Has adequate organ function * Male participants agree to protocol-specified contraception requirements including refraining from donating sperm and using protocol-specified contraceptives unless confirmed to be azoospermic * Female participants must not be pregnant or breastfeeding, and must agree to protocol-specified contraceptive requirements and must have a negative highly sensitive pregnancy test within 24 hours (for a urine test) or 72 hours (for a serum test) before the first dose of study intervention For Arm 1 - Has locally advanced unresectable or metastatic solid-tumor malignancy with histologically OR blood-based confirmation of KRAS G12C mutation who has received at least 1 line of therapy for systemic disease For Arm 2 \- Has an untreated metastatic non-small cell lung cancer (NSCLC) with histologically OR blood-based confirmation of KRAS G12C mutation and histologic confirmation of programmed cell death ligand 1 (PD-L1) tumor proportion score (TPS) ≥1% For Arm 3 * Has locally advanced unresectable or metastatic solid-tumor malignancy with histologically or blood-based confirmation of KRAS G12C mutation who has received at least 1 line of therapy for systemic disease Expansion Group A: 2L+NSCLC * Has histologically or cytologically confirmed diagnosis of unresectable or metastatic NSCLC with histological or blood-based confirmation of KRAS G12C mutation and submits archival tumor sample * Previous treatment failure of at least 1 line of systemic therapy Expansion Group B * Has locally advanced unresectable or metastatic solid-tumor malignancy, excluding NSCLC or CRC, with histologically or blood- based confirmation of KRAS G12C mutation who has received at least 1 line of therapy for systemic disease Arm 4 only - Has an untreated advanced or metastatic nonsquamous NSCLC with histologically or blood-based confirmation of KRAS G12C mutation Arm 5 only * Histologically or cytologically confirmed diagnosis of locally advanced unresectable or metastatic colorectal adenocarcinoma and with histologically or blood-based confirmation of KRAS G12C mutation * Previous treatment failure of one or 2 previous line(s) of systemic therapy Arm 6 only \- Locally advanced unresectable or metastatic colorectal adenocarcinoma with histologically or blood-based confirmation of KRAS G12C mutation Exclusion Criteria: * Has received chemotherapy, definitive radiation, or biological cancer therapy within 4 weeks (2 weeks for palliative radiation) before first dose of study intervention * Has a history of second malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 5 years * Has clinically active central nervous system (CNS) metastases and/or carcinomatous meningitis * Has an active infection requiring systemic therapy * Known history of HIV infection or. has a known history of Hepatitis B virus or known active Hepatitis C virus infection * Has a history of interstitial lung disease, noninfectious pneumonitis requiring active steroid therapy, or ongoing pneumonitis * Has an active autoimmune disease requiring systemic therapy * Has not fully recovered from any effects of major surgical procedure without significant detectable infection * Has one or more of the following ophthalmological findings/conditions: intraocular pressure \>21 mm Hg and/or any diagnosis of glaucoma; diagnosis of central serous retinopathy, retinal vein occlusion, or retinal artery occlusion and/or a diagnosis of retinal degenerative disease * Has received live or live-attenuated vaccine within 4 weeks of study start Arm 4 Only * Is unable to interrupt aspirin or other nonsteroidal anti-inflammatories (NSAIDs), other than an aspirin dose ≤1.3 grams per day, for at least 2 days (5 days for long-acting agents \[for example, piroxicam\]) before, during, and for at least 2 days after administration of pemetrexed. * Is unable/unwilling to take folic acid, vitamin B12, and dexamethasone