This study is a prospective multicenter randomized controlled Interventional study, to assess the clinical efficacy and safety of corticosteroids compared to corticosteroids in combination with Ruxolitinib in the treatment of severe checkpoint inhibitor pneumonitis.

Inclusion Criteria:

1. 18 years old≤ Aged ≤80 years old.
2. Diagnosis of malignancy.
3. Malignant tumors initially treated with immune checkpoint inhibitors (antibodies targeting PD-1, PD-L1, CTLA-4, or new immune checkpoint inhibitors) in combination with or without chemotherapy.
4. Diagnosis of grade 3 or 4 CIP: CIP severity at CTCAE grade 3 or 4.
5. Patients who and whose family members understand the study protocol, are willing to participate in the study and could provide written informed consent.

Exclusion Criteria:

1. Predicted life expectancy<12 weeks.
2. Any evidence of active or uncontrolled viral infection, including hepatitis B, hepatitis C and human immunodeficiency virus (HIV), or any clinical signs of bacterial, other viral, parasitic or fungal infection requiring treatment.
3. malignancy progression.
4. Patients with other serious complications that may affect safety or adherence judged by the investigator.
5. Any significant clinical and laboratory abnormalities judged by investigator that affect the safety evaluation.
6. Patients can't fully understand the study protocol, arrangement and other study-related elements.
7. Patients with evidence of severe liver or kidney dysfunction judged by investigator unsuitable for enrolment.
8. Women who are pregnant, breast feeding or unable to use effective contraception during the study period and for 3 months after the completion.
9. Patients who cannot comply with study treatment and follow-up according to the trial protocol.