Because most patients with R/M NPC have received long-term maintenance of immunotherapy at the time of initial treatment and the first-line treatment, there are a large number of PD-1 inhibitor refractory patients. How to deal with the ICIs resistance is an urgent problem in clinical practice.

Inclusion Criteria:

1. Had histopathologically confirmed nonkeratinizing recurrent/metastatic NPC.
2. ECOG performance status of 0 or 1.
3. Progression after previous treatment with platinum-based dual-drug chemotherapy.
4. Progression after previous treatment with PD-1 inhibitors.
5. Experieced at least 1 line systemic therapy.
6. Subjects enrolled must have measurable lesion(s) according to response evaluation criteria in solid (RECIST) v1.1.
7. Adequate organ function assessed by laboratory parameters during the screening period.
8. Life expectancy more than 12 weeks.
9. Able to understand and sign an informed consent form (ICF).
10. Able to swallow the pill.

Exclusion Criteria:

1. Recurrent lesions suitable for radical treatment (radiotherapy or surgery).
2. Previous treatment over 3 lines.
3. Prior use of CDK4/6 inhibitors.
4. Patients with other malignancies.
5. Patients with known or suspected autoimmune diseases including dementia and seizures.
6. Multiple factors affecting the absorption of oral medications (e.g., dysphagia, chronic diarrhea, and bowel obstruction).
7. An excessive dose of glucocorticoids given within 4 weeks before enrollment.
8. Complications requiring long-term use of immunosuppressive drugs or systemic or local use of immunosuppressive-dose corticosteroids.
9. Patients with active pulmonary tuberculosis (TB) receiving anti-TB treatment or who have received anti-TB treatment within 1 year prior to screening.
10. HIV positive; HBsAg positive and HBV DNA copy number positive (quantitative detection ≥ 1000 cps/ml); chronic hepatitis C with blood screening positive (HCV antibody positive).
11. Any anti-infective vaccines such as influenza vaccine, varicella vaccine, etc., within 4 weeks before enrollment.
12. Women of childbearing age with a positive pregnancy test and lactating women.