Study Overview: This study looks at a medicine called Bezuclastinib for people with a condition called Advanced Systemic Mastocytosis (AdvSM). AdvSM is a disease where certain blood cells grow too much. This study has two parts and is open-label, meaning everyone knows what treatment they are getting.

Eligibility: Patients can join if they have AdvSM, including types like Aggressive Systemic Mastocytosis (ASM), Systemic Mastocytosis with Associated Hematologic Neoplasm (SM-AHN), or Mast Cell Leukemia (MCL). They must meet certain health requirements and can't have certain other health issues, like ongoing toxicity from previous treatments.

Study Exclusions: You cannot join if you have unresolved side effects from previous treatments, specific heart conditions, or certain infections like HIV or hepatitis.

• Study Duration: The study is in Phase 2 and will be conducted in two parts.
• Visits: Participants will have regular visits and tests to monitor their health and the effects of the medicine.
• Risks: Possible risks include side effects from Bezuclastinib or worsening of health conditions.