The purpose of this expanded access program (EAP) protocol is to provide investigational bezuclastinib to patients with a diagnosis of nonadvanced systemic mastocytosis (NonAdvSM) or advanced systemic mastocytosis (AdvSM) who have received and failed or been intolerant to at least one standard approved therapy and/or have no comparable or satisfactory alternative therapy options.

Key Inclusion Criteria:

• Able to provide written informed consent and commit to EAP assessments.
• ≥18 years of age.
• Able to swallow tablets.
• Diagnosed with ASM, SM-AHN, MCL, BMM, ISM, or SSM according to the 2022 WHO Classification for SM
• Not receiving adequate disease control on current therapy(ies).
• Have clinically acceptable laboratory screening results.

Exclusion Criteria:

• Patients who are eligible for and/or enrolled in an on-going bezuclastinib clinical trial.
• Patients who discontinued investigational use of bezuclastinib in previous clinical trials due to toxicity or withdrawal of consent.
• Pregnant or currently breastfeeding.
• Prior or ongoing clinically significant illness or medical or physical condition

Other protocol-defined criteria apply.