This open-label, single-arm clinical trial is to evaluate the safety and effectiveness of KC1036 in treating adolescents aged 12 and above with advanced Ewing sarcoma. Participants will take KC1036 once daily, with each treatment cycle lasting 4 weeks.

Inclusion Criteria:

• Age between 12 and less than 18 years;
• Diagnosed with Ewing sarcoma confirmed by histopathological examination;
• Patients with locally advanced or metastatic Ewing sarcoma that is unresectable or has failed standard treatment, and for whom no other treatment options are available as assessed by the investigator;
• Body weight of ≥30 kg;
• Karnofsky performance status (≥16 years) or Lansky performance status (<16 years) score of ≥60%;
• Patients with at least one measurable lesions according to RECIST v1.1 (Response Evaluation Criteria in Solid Tumors);
• Expected survival of more than 12 weeks;
• Sufficient organ and bone marrow function;
• Female patients who have started menstruating must have a negative pregnancy test;
• The patient and their legal guardians understand and are willing to participate in the trial, and have signed the informed consent form.

Exclusion Criteria:

• Patients with primary central nervous system tumors;
• Presence of central nervous system metastases as diagnosed by imaging;
• History of or concurrent other malignancies within the past 5 years;
• Gastrointestinal abnormalities;
• Cardiovascular or cerebrovascular abnormalities;
• Patients who have previously received VEGFR-TKI small molecule treatment;
• Currently participating in another therapeutic clinical trial; received any anticancer treatment within 2 weeks or 5 half-lives (whichever is longer) before the start of the study treatment; received whole-brain radiation therapy within 14 days before the start of the study treatment; received stereotactic radiosurgery within 7 days before the start of the study treatment; or received herbal or traditional Chinese medicine for anticancer purposes within 2 weeks before the study treatment;
• Underwent major surgery within 2 months before enrollment or have not fully recovered, or plan to undergo surgery during the current study period;
• Persistent toxicity from previous anticancer treatment that has not improved to ≤ Grade 1 (according to CTCAE v5.0), excluding alopecia;
• Unhealed skin wounds, surgical sites, traumatic sites, severe mucosal ulcers, or fractures;
• Uncontrolled significant pleural effusion, ascites, or pericardial effusion;
• Active bacterial, viral, or fungal infections; unexplained fever >38.5°C within 2 weeks before enrollment;
• Hepatitis B surface antigen (HBsAg) positive with HBV-DNA ≥500 IU/mL or 2500 copies/mL; Hepatitis C virus (HCV) antibody positive with HCV RNA ≥200 IU/mL or positive test results; HIV-positive individuals;
• Presence of psychiatric or neurological disorders; or cognitive impairment;
• Fertile patients (e.g., females who have started menstruating or males who have started ejaculating) who do not agree to use contraception (e.g., birth control pills or condoms) during the study and for 6 months after the study ends;
• Patients with insufficient compliance as evaluated by investigator;
• The investigator believes that it is not suitable to patient in this clinical trial.