• Patients who are aged ≥ 18 years.

• Gastrointestinal stromal tumors confirmed by histopathological examination, and CD- and/or DOG-1-positive by immunohistochemistry.

• Presence of mRECIST v1.1-compliant lesions with at least one measurable lesion (non-lymphadenopathy ≥1.0 cm or ≥2-fold scan slice thickness).

• Treatment with Avapritinib.

• Patients with an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 2 at screening.

• Patient informed consent and signed written consent form.

• The patient was compliant and voluntarily scheduled for follow-up, treatment, laboratory tests, and other study procedures.