Efficacy and Safety of Becotatug Vedotin (MRG003) Combined With Anti-PD1 as Maintenance Therapy for Recurrent and Metastatic Nasopharyngeal Carcinoma

Inclusion Criteria: * Aged between 18 and 75 years at diagnosis, regardless of gender; * Histologically confirmed nasopharyngeal carcinoma; * Patients with advanced nasopharyngeal carcinoma with confirmed distant metastasis (Stage IVb per AJCC 8th edition; Stage IV per AJCC 9th edition), or recurrent nasopharyngeal carcinoma unsuitable for locoregional or curative therapy; * Achieved stable disease (SD) assessed per RECIST v1.1 or maintained positive plasma EBV DNA after 4 to 6 cycles of first-line chemotherapy combined with immunotherapy; * Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1; * Expected survival of at least 12 weeks; * No prior systemic chemotherapy administered within 6 months before diagnosis (excluding patients with disease progression more than 6 months after neoadjuvant chemotherapy, adjuvant chemotherapy, or definitive concurrent chemoradiotherapy); * At least one measurable lesion as defined by RECIST v1.1; * Adequate organ and bone marrow function as defined below: 1. HGB ≥90 g/L, WBC ≥4×10⁹/L, PLT ≥100×10⁹/L. 2. Liver function: TBIL \<1.5 × ULN; ALT and/or AST \<2.5 × ULN. For patients with liver metastases, ALT or AST \<5 × ULN. For patients with liver or bone metastases, ALP \<5 × ULN. 3. Renal function: creatinine \<1.5 × ULN. 4. Coagulation: INR of PT / PTT \<1.5 × ULN; * Able to provide written informed consent and comply with all protocol-specified procedures including laboratory tests and follow-up visits; * Female subjects of childbearing potential and male subjects with childbearing potential partners must agree to use effective contraception from screening through 6 months after the last dose of study treatment (e.g., condoms, regular oral contraceptives as prescribed). Exclusion Criteria: * Peripheral neuropathy ≥ Grade 2 (per NCI-CTCAE v5.0); * History of hypersensitivity to any study drug; * Expected survival less than 3 months; * Active hepatitis B (positive HBsAg or HBcAb with HBV DNA ≥ 2000 IU/mL) or active hepatitis C (positive HCV antibody with HCV RNA above the lower limit of quantification at the study site). For patients with normal liver function receiving antiviral therapy, eligibility shall be determined by the investigator; * Patients with positive HIV antibody; * Active bacterial, fungal, viral infection requiring systemic treatment, or interstitial pneumonia within 1 week prior to the first administration of study drugs; * Received anti-tumor therapies including chemotherapy, small-molecule inhibitors, immunotherapy (e.g., interleukins, interferons, thymosins) within 4 weeks or 5 half-lives (whichever is shorter, with a minimum interval of 2 weeks) before the first dose of study drugs; * Received anti-tumor therapies including chemotherapy, small-molecule inhibitors, immunotherapy (e.g., interleukins, interferons, thymosins) within 4 weeks or 5 half-lives (whichever is shorter, with a minimum interval of 2 weeks) before the first dose of study drugs; * Underwent major surgery within 3 months prior to the first dose, or planned to receive major surgery during the study period; * Severe thromboembolic events within 6 months before screening, such as cerebrovascular accidents (including transient ischemic attack) and pulmonary embolism; * Active malignant tumors within 2 years prior to the first administration of study drugs, excluding nasopharyngeal carcinoma under investigation and any locally curable tumors that have received radical treatment (e.g., resected basal cell or squamous cell skin cancer, superficial bladder cancer, cervical or breast carcinoma in situ); * Severe cardiovascular diseases within 6 months before enrollment, including but not limited to: 1. Acute myocardial infarction, unstable angina, coronary angioplasty or stenting, deep vein thrombosis, stroke; 2. New York Heart Association (NYHA) Class III or IV congestive heart failure, or left ventricular ejection fraction (LVEF) \< 50%; 3. Electrocardiogram (ECG) abnormalities of significant clinical relevance at screening as assessed by the investigator; * Pregnant or breastfeeding women; * Presence of any severe and/or uncontrolled diseases that, in the investigator's judgment, may interfere with the patient's participation in the study (including but not limited to uncontrolled diabetes, dialysis-dependent renal disease, severe liver disease, life-threatening autoimmune and hemorrhagic diseases, substance abuse, neurological disorders); * Any other conditions deemed inappropriate for participation by the investigator.