Phase 1/2 Trial of S241656 in Selected RAS/MAPK Mutation- Positive Malignancies

Key Inclusion Criteria: * Life expectancy of ≥ 12 weeks in the opinion of the investigator. * Histologically or cytologically confirmed recurrent locally advanced (unresectable) or metastatic solid tumors with documented RAS or RAF mutations or alterations. * Adequate bone marrow and organ function. * Recovered from toxicity to prior anti-cancer therapy. Part 1 Dose Escalation cohort ONLY: * Part 1A: Advanced/metastatic NSCLC with KRAS non-G12C, HRAS, NRAS, BRAF or CRAF (RAF1) mutations or alterations * Part 1B: Advanced/metastatic GI tumors (e.g., PDAC, CRC, and BTC) with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations * Part 1C: Advanced/metastatic PDAC with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations * Part 1D: Colorectal adenocarcinoma with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations * Part 1E: Other advanced/metastatic non-GI, non-NSCLC solid tumors with KRAS, HRAS, NRAS, BRAF, CRAF (RAF1) mutations or alterations Part 2 Dose Optimization and Expansion cohorts ONLY: * Part 2A: Advanced/metastatic NSCLC with KRAS non-G12C mutations and/or BRAF mutations * Part 2A1: Advanced/metastatic NSCLC with KRAS non-G12C mutations * Part 2A2: Advanced/metastatic NSCLC with BRAF mutations * Part 2A3: Advanced/metastatic NSCLC with KRAS non-G12C or BRAF mutations or alterations and active CNS metastatic disease * Part 2A4: Advanced/metastatic NSCLC with a KRAS G12C mutation * Part 2B1: Advanced/metastatic PDAC with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations * Part 2B2: Advanced/metastatic CRC with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations * Part 2B3: Advanced/metastatic BTC (adenocarcinoma) with KRAS, HRAS, NRAS, BRAF, and/or CRAF (RAF1) mutations or alterations Key Exclusion Criteria: * Cancer that has a known MEK1/2 mutation. * Known allergy/hypersensitivity to excipients of S241656 or to any of the registered IMPs administered in combination. * Any contra-indication, to use of any of the combination chemotherapy or anti-EGFR therapy partners administered as part of this trial. * Major surgery within 4 weeks of study entry or planned during study. * Ongoing anticancer therapy. * Ongoing radiation therapy. * Uncontrolled or active clinically relevant bacterial, fungal, or specific viral infection requiring systemic therapy. * Clinically significant cardiovascular disease. * Symptomatic spinal cord compression. * Evidence of active malignancy (other than study-specific malignancies) requiring systemic therapy within the next 2 years. * History or current evidence of retinal vein occlusion (RVO) or current risk factors for RVO. * Females who are pregnant or breastfeeding. * Actively receiving systemic treatment or direct medical intervention on another therapeutic clinical study. * Prior use of experimental agents that target the KRAS/BRAF/MEK/ERK pathway.