HSK42360-Na Tablets Combined With Cetuximab With or Without Chemotherapy in BRAF V600-Mutant Metastatic Colorectal Cancer

This is a prospective, multi-center, single-arm, open-label Phase I/II clinical study. The study consists of two stages: Phase I (Dose Escalation): A 3+3 dose escalation design with 3 pre-specified dose levels of HSK42360-Na tablets (1200 mg QD, 1200 mg BID, 1200 mg TID) in combination with cetuximab (500 mg/m2 IV every 2 weeks). Each dose level enrolls 3-6 evaluable participants. A 28-day cycle comprises the DLT observation period. Backfill cohorts of approximately 6-18 participants per dose level may be enrolled after safety confirmation. The primary objectives are to evaluate safety, tolerability, and determine the DLT, MTD, and RP2D. Phase II (Cohort Expansion): After RP2D determination, three expansion cohorts are planned: * Cohort 1: HSK42360-Na + cetuximab (approximately 42 participants with prior systemic therapy) * Cohort 2: HSK42360-Na + cetuximab + mFOLFOX6 (6-9 safety run-in + approximately 36 expansion) * Cohort 3: HSK42360-Na + cetuximab + FOLFIRI (6-9 safety run-in + approximately 36 expansion) Participants continue treatment until disease progression, unacceptable toxicity, withdrawal of consent, or other termination criteria. Tumor assessment is performed every 6 weeks (every 8 weeks after 18 months) per RECIST 1.1. Safety follow-up occurs 30 days after the last dose, and survival follow-up is conducted every 3 months thereafter.