The purpose of this study is to observe the clinical efficacy and safety of Durvalumab combined with intrathecal chemotherapy in non-small cell lung cancer with leptomeningeal metastasis

Inclusion Criteria:

1. Male and Female age 18 or more
2. Pathologically proven non-small cell lung cancer
3. MRI(Magnetic Resonance Imaging,MRI) imaging findings or the detection of malignant cells in cerebrospinal fluid
4. Patients have the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

1. KPS score <60
2. History of autoimmune diseases
3. With severe hepatic and renal dysfunction
4. Has a history of (non-infectious) pneumonitis that required steroids