Study of TL-895 in Subjects With Myelofibrosis or Indolent Systemic Mastocytosis

This study evaluates TL-895, a potent, orally-available and highly selective irreversible tyrosine kinase inhibitor for the treatment of Myelofibrosis (Cohorts 1-3) or Indolent Systemic Mastocytosis (Cohort 5). Participants must be diagnosed with Myelofibrosis and be relapsed/refractory (e.g., having failed prior therapy), intolerant, or ineligible to receive JAKi treatment, or be diagnosed with Indolent Systemic Mastocytosis.

Cohorts 1-3 Key Inclusion Criteria: * Adults ≥18 years of age * Confirmed diagnosis of PMF, post-PV MF, or post-ET MF, as assessed by treating physician according to the World Health Organization (WHO) criteria * Eastern Cooperative Oncology Group (ECOG) performance status of ≤2 * Adequate hematologic, hepatic, and renal functions * MF symptoms as defined by having at least 2 symptoms with an average baseline (Day -7 to Day -1) score of at least 1 for each of the 2 symptoms per MFSAF v4.0 * Cohort 3 only: Ineligibility for JAKi treatment with a platelet count of ≥ 25 and \< 50 x 10\^9/L Key Exclusion Criteria: * Prior treatment with any BTK or BMX inhibitors * Prior treatment with JAKi within 28 days prior to study treatment * Prior splenectomy or splenic irradiation within 24 weeks prior to first dose of study treatment Cohort 5 Key Inclusion Criteria: * Adults ≥18 years of age * Confirmed diagnosis of ISM as defined by WHO diagnostic criteria based on review of bone marrow biopsy pathology report results * Subject must have moderate-to-severe symptoms Key Exclusion Criteria: * Prior treatment with any BTK or BMX inhibitors * Prior treatment with Avapritinib, bezuclastinib, or BLU-263/elenestinib * Diagnosis with another myeloproliferative disorder