Clinical Study of Mitoxantrone Hydrochloride Liposome Injection Combined With Capecitabine Versus Capecitabine Monotherapy in Patients With Recurrent Metastatic Nasopharyngeal Carcinoma Who Failed Platinum-containing Treatment

Inclusion Criteria: 1. Willing to participate in the study and sign the informed consent form (ICF). 2. Age ≥ 18 years. 3. Nasopharyngeal carcinoma confirmed by histopathology. 4. Recurrent metastatic nasopharyngeal carcinoma that has previously failed treatment with first-line platinum-containing standard regimens and/or second-line standard regimens. 5. At least one evaluable lesion at baseline according to RECIST 1.1 criteria; The area should not have received previous radiotherapy, or there is evidence that the lesion has made definite progress after radiotherapy. 6. Eastern Cooperative Oncology Group (ECOG) score 0-1. 7. Toxic reaction caused by any previous antitumor treatment has recovered to grade 1 or below (except for alopecia, pigmentation, or other toxicities deemed by the investigator to pose no safety risk to the patient). 8. Adequate main organ function. 9. Female patients must have a negative blood HCG test (except for menopause and hysterectomy), Female patients of childbearing age and their partners must use effective contraception (For example: combination hormones \[containing estrogen and progesterone\] to suppress ovulation, progestogen contraception to suppress ovulation, intrauterine device, intrauterine hormone release system, bilateral tubal ligation, vasectomy, avoidance of sexual activity, etc) during the trial and within 6 months of the end of the last dose. 10. Male patients and their partners agree to use one of the contraceptive measures described in Article 9. Exclusion Criteria: 1. Severe allergy to mitoxantrone or liposome; Previous severe, unexpected reactions to fluorouracil or known allergy to fluorouracil or to any excipients of capecitabine. 2. Previous treatment regimens containing capecitabine for recurrent or metastatic nasopharyngeal carcinoma; Patients with locally advanced nasopharyngeal carcinoma have previously experienced disease recurrence or metastasis during or within 6 months of use of capecitabine. 3. Patients with brain or meningeal metastasis. 4. Expected lifetime \< 3 months. 5. Patients with active hepatitis B, hepatitis C or HIV. 6. Active bacterial infection, fungal infection, viral infection, or interstitial pneumonia requiring systemic therapy within 1 week prior to the first administration of the study drug. 7. Antitumor therapy such as chemotherapy, small-molecule inhibitors, immunotherapy (such as interleukin, interferon, or thymosin) within 4 weeks or 5 half-lives (whichever is shorter but at least 2 weeks) prior to initial administration of the study drug; Received Chinese patent drugs with antitumor activity within 14 days prior to administration. 8. Have received other investigational drugs within 4 weeks prior to initial administration. 9. Patients had major surgery within 3 months prior to initial dosing or plan to have major surgery during the study period. 10. Severe embolic events, such as cerebrovascular accidents (including transient ischemic attacks) and pulmonary embolism, occurred within 6 months prior to screening. 11. Other active malignant tumors within 2 years prior to the first study drug administration. 12. Abnormal heart function, including: Long QTc syndrome or QTc interval \>480 ms; Complete left bundle branch block, second-degree or third-degree atrioventricular block; Severe, uncontrolled arrhythmias requiring medication; History of chronic congestive heart failure with NYHA ≥ grade 3; Cardiac ejection fraction less than 50% or lower than the lower limit of the laboratory test range within 6 months prior to screening; CTCAE version 5.0 ≥ grade 3 valvular heart disease; Uncontrolled hypertension (defined as measuring systolic blood pressure \>160 mmHg or diastolic blood pressure \>90 mmHg when medically controlled); Myocardial infarction, unstable angina, history of severe pericardial disease, ECG evidence of acute ischemic or active conduction system abnormalities within 6 months prior to screening. 13. Prior treatment with doxorubicin or other anthracyclines and the cumulative doxorubicin doses greater than 350 mg/m\^2 (anthracycline equivalent: 1 mg doxorubicin = 2 mg epirubicin = 2 mg daunorubicin = 0.5 mg normethoxydaunorubicin = 0.45 mg mitoxantrone). 14. Pregnant or lactating women. 15. Have any serious and/or uncontrollable medical conditions that, as determined by the investigator, may affect the patient's participation in the study. 16. Have severe gastrointestinal disorders that affect the ingestion, transport, or absorption of medications. 17. Other situations that the investigator determines to be inappropriate for participation.