This is a multicenter, single arm, open label phase II clinical study in China. This study will evaluate the efficacy and safety of ABSK021 (Pimicotinib) in the treatment of patients with cGvHD who failed first-line therapy.

This is a phase II, open-label study to evaluate safety, tolerability, pharmacokinetics (PK), and clinical benefit of ABSK021 in patients with hormone refractory or relapsed cGvHD. This study consisted of Part A and Part B, all cGvHD patients in this study will receive continuous oral treatment with ABSK021 once a day (QD) in a 28-day cycle, complete the core treatment period and extended treatment period, and receive regular follow-up until the termination of treatment is determined.

Inclusion Criteria:

1. Sign the informed consent and agree to comply with the requirements and restrictions set out in the informed consent.
2. At the time of signing the informed consent., the patient must be at least 18 years old, regardless of gender ；
3. Allogeneic hematopoietic stem cell transplantation from any donor source using bone marrow, peripheral blood stem cells, or cord blood.
4. Patients who have received at least 1 line of systemic therapy
5. If the patient is being treated with glucocorticoids or calcineurin inhibitor(CNI), the patient should have received a stable dose of the above treatment for not less than 2 weeks prior to the first use of ABSK021.
6. ECOG (Eastern Cooperative Oncology Group Performance Status) physical strength score 0-2;7. The patient had sufficient organ and bone marrow function within 14 days prior to the first use of ABSK021.

8. For patients with Part A only: antifungal drugs that are currently being used in combination with CYP3A4 potent inhibitors should have been continuously used in accordance with regulations for no less than one week before the first use of ABSK021

Exclusion Criteria:

1. In previous treatment, he received highly selective colony stimulating factor 1 receptor (CSF-1R) targeted therapy, including small molecule or large molecule drugs;
2. A known history of allergy to components of the investigational drug composition ;
3. Patients continued to use CYP3A4 in combination with antifungal agents or in the two weeks prior to the initial administration of ABSK021 Strong inducer;
4. The patient has received more than 5 lines of systemic therapy for cGvHD;
5. The patient presented with aGvHD symptoms without cGvHD symptoms ;
6. Any evidence of potential tumor or recurrence of post-transplant lymphoproliferative disease at the screening stage .
7. There are factors that have been determined by the investigators to have a significant influence on oral drug absorption
8. Present with cholestatic disease, or unresolved hepatic sinus obstruction syndrome/venous obstructive disease;
9. active infection.
10. During the screening period, the investigators judged that the patients had insufficient pulmonary function reserve, with FEV1≤ 39% or pulmonary function classification score of 3;
11. Prior treatment (adverse events did not return to ≤ Grade 2 (CTCAE v5.0);
12. Pregnant or lactating women;
13. Patients who are unable to or disagree with contraception.