Dual EGFR/HER2 Blockade Combined With Irinotecan for the Treatment of HER2-Positive Metastatic Colorectal Cancer

Inclusion Criteria: * Signed and dated informed consent must be obtained voluntarily from the subject prior to performing any study-related procedures (non-routine care), in accordance with regulatory and institutional guidelines. * 18 to 75 years of age, inclusive. * Histologically or cytologically confirmed adenocarcinoma of the colon or rectum with evidence of distant metastasis. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * HER2-positive tumor with wild-type KRAS, NRAS, and BRAF genes confirmed by testing at any time prior to screening. HER2 positivity is defined as: Immunohistochemistry (IHC) showing HER2 3+ staining in \>50% of tumor cells; or HER2 2+ by IHC with positive fluorescence in situ hybridization (FISH): HER2/CEP17 ratio ≥2.0 in \>50% of tumor cells; or Next-generation sequencing (NGS) of tissue or circulating tumor DNA (ctDNA) demonstrating HER2 copy number ≥6. * Adequate organ function as evidenced by: Absolute neutrophil count ≥1.5×10\^9/L Platelet count ≥75×10\^9/L Serum total bilirubin ≤1.5×upper normal limit (UNL) Aspartate aminotransferase (AST) ≤2.5×UNL Alanine aminotransferase (ALT) ≤2.5×UNL Serum creatinine ≤1.5×UNL * Disease progression after prior treatment with fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy, including: Subjects who received oxaliplatin in the adjuvant setting must have experienced disease progression within 6 months after completing adjuvant therapy.Patients who decline standard therapy due to intolerable toxicity are eligible. * Presence of at least one measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. * Willing and able to comply with the study protocol and visit schedule Exclusion Criteria: * Known KRAS, NRAS, or BRAF mutations detected by ctDNA testing prior to enrollment; or tumors with mismatch repair deficiency (dMMR) or high microsatellite instability (MSI-H). * Concurrent intestinal obstruction, active bleeding, or perforation requiring emergency surgery. * Major surgery (e.g., laparotomy, thoracotomy, or organ resection via laparoscopy) or significant trauma within 4 weeks prior to study entry (surgical incision must be fully healed before enrollment). * Active coronary artery disease within 12 months before screening, including severe/unstable angina, newly diagnosed angina, or myocardial infarction. * History of thrombosis or embolism within 6 months, including cerebrovascular accident (transient ischemic attack included), pulmonary embolism, or deep vein thrombosis. * Congestive heart failure classified as New York Heart Association (NYHA) Class II or higher. * HIV infection or AIDS; untreated active hepatitis (HBV-DNA ≥500 IU/mL for hepatitis B; detectable HCV-RNA for hepatitis C); or HBV/HCV co-infection. * Interstitial lung disease, non-infectious pneumonitis, or uncontrolled systemic diseases (e.g., diabetes, hypertension, pulmonary fibrosis, acute pneumonia). * Persistent ≥Grade 2 toxicities (per CTCAE v5.0) from prior therapies (excluding peripheral neuropathy, anemia, alopecia, or skin hyperpigmentation). * Known or suspected hypersensitivity to any study drugs. * Pregnancy or lactation.