A Study to Evaluate MRG003 vs Cetuximab/Methotrexate in in the Treatment of Patients With RM-SCCHN

Inclusion Criteria: \- 1. Understands and provides written informed consent and willing to follow the requirements specified in protocol. 2\. Age: ≥18 years and ≤75 years. 3. Life expectancy: ≥3 months. 4. Must have histologically or cytologically confirmed recurrent or metastatic squamous cell carcinoma of the head and neck (including oral cavity, oropharynx, hypopharynx, larynx) who had previously failed PD-1 (L1) inhibitors and platinum-based therapy (in combination or sequential). Prior therapies should be no more than 2 lines. Note: If disease progression occurred during neoadjuvant/adjuvant treatment or concurrent radiotherapy, or within 6 months after treatment discontinuation, the anti-tumor therapies (including platinum-based chemotherapy, anti-EGFR monoclonal antibody, PD-1 (L1) inhibitors, etc.) during neoadjuvant/adjuvant treatment or concurrent radiotherapy is counted as one line of prior treatment. Discontinuation or dose reduction of one drug, or change of platinum- or fluorouracil-based agents or PD-1 (L1) inhibitors without disease progression is considered as the same line of treatment. 5\. Must have at least one measurable lesion per RECIST v1.1. Previously irradiated lesion cannot be considered as target unless there is documented progression three months after the last treatment of radiotherapy. 6\. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 (Appendix 1) with no deterioration within 2 weeks prior to enrollment. 7\. Adequate bone marrow function, defined as meeting all of the following criteria and having no transfusion therapy within 3 weeks (21 days) or growth factors (G-CSF, EPO, etc.) support within 2 weeks (14 days) prior to dosing: • Hemoglobin (Hb) ≥ 9.0 g/dL (90 g/L) • Absolute neutrophil count (ANC) ≥ 1,500/mcL (1.5 × 109/L) • Total platelet count (PLT) ≥ 100,000/mcL (100 × 109/L) 8. Adequate hepatic function, defined as all of the following: • Total bilirubin (TBIL) ≤ 1.5×ULN; • Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5×ULN if no liver metastasis; ALT or AST ≤ 3.0×ULN in the presence of liver metastasis; • Alkaline phosphatase (ALP) ≤ 1.5×ULN; ≤ 2×ULN in the presence of liver metastasis; • Serum albumin ≥ 30 g/L 9. Coagulation: International Normalized Ratio (INR) or prothrombin time (PT), activated partial thromboplastin time (APTT) ≤ 1.5×ULN (unless patient is receiving anticoagulant therapy whose anticoagulant level should be within the therapeutic range). The laboratory parameters should be closely monitored by investigator if the patient is on anticoagulation therapy. 10\. Adequate renal function, defined as Creatinine ≤ 1.5×ULN or creatinine clearance rate (Ccr) ≥ 50 mL/min if Creatinine \> 1.5×ULN (Creatinine clearance is calculated using the modified Cockcroft-Gault equation. Creatinine clearance can be calculated as Ccr = \[(140-age) × body weight (kg) × (0.85 for women only)\]/(72 × serum creatinine) if no local guidelines are available (without significant electrolyte imbalance that is not easily corrected). 11\. Baseline Left Ventricular Ejection Fraction (LVEF) ≥ 50% measured by multiple-gated acquisition (MUGA) or echocardiogram (ECHO). 12\. A negative serum or urine pregnancy test within 7 days prior to the first dose of study treatment (females of childbearing potential). If urine pregnancy test is positive or cannot be confirmed as negative, a confirmatory serum pregnancy test is required. 13\. Patients, both females and males, of reproductive potential must agree to use adequate contraception during study treatment and for 180 days after the last treatment. 1. Females of childbearing potential (who are not surgically sterile or postmenopausal for \< 1 year) who are willing to use adequate and reliable contraception such as avoidance of heterosexual activity, sterilization, oral contraceptives, injectable contraceptives, intrauterine devices, condoms, etc., during the study until 180 days after the last dose of study drug. 2. Male patients who are willing to use latex condoms during any sexual contact with females of childbearing potential during treatment until 180 days after the last treatment, even if vasectomy has been successfully performed. Reservation of semen specimen prior to the first dose of study treatment is recommended for fertile males for potential future conception. Exclusion Criteria: * 1\. Grade ≥2 peripheral neuropathy per CTCAE v5.0. 2. Is expected to require surgery or any other form of systemic or local anti-tumor therapy during the study, including maintenance therapy or radiotherapy (including palliative therapy, except for palliative therapy for non-target lesions) for SCCHN. 3\. Received systemic chemotherapy within 3 weeks, small molecule targeted therapy within 2 weeks or 5 half-lives (whichever is longer), biological anti-tumor therapy, macromolecule targeted therapy or immunotherapy within 4 weeks before the first dose of study treatment, or major surgery (except for minor surgery within 2 weeks and fully recovered); radiotherapy (except radiotherapy for CNS, wash-out period ≥ 28 days is required) within 14 days before the first dose of study treatment. 4\. Known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Patients with brain metastases may participate provided they are treated and stable, and do not have the following: * Progressive or new neurological deficits, seizures, evidence of increased intracranial pressure, vomiting, or headache; * Evidence of enlarging brain metastases by MRI at least 4 weeks prior to the first dose and corticosteroids is required for at least 14 days prior to study drug treatment. 5\. Residual toxicities (except alopecia, fatigue, and Grade 2 hypothyroidism) due to prior anti-tumor therapy (including immunotherapy, targeted therapy, chemotherapy or radiotherapy) or ≥ Grade 1 (CTCAE v5.0) clinically significant laboratory abnormality.