(EXPLORER) Study of BLU-285 in Patients With Advanced Systemic Mastocytosis (AdvSM) and Relapsed or Refractory Myeloid Malignancies

Inclusion Criteria: For Part 1:Patients must have one of the following diagnoses based on World Heath Organization (WHO) diagnostic criteria: * Aggressive systemic mastocytosis (ASM). * Systemic mastocytosis with an associated hematologic neoplasm (SM-AHN) and at least 1 C-finding attributable to systemic mastocytosis (SM). The AHN must be myeloid, with the following exceptions that are excluded: Acute myeloid leukemia (AML), Myelodysplastic syndrome (MDS) that is very high- or high-risk as defined by the International prognostic scoring system for myelodysplastic syndromes (IPSS-R) and Philadelphia chromosome positive malignancies. * Mast cell leukemia (MCL). * Histologically- or cytologically- confirmed myeloid malignancy that is relapsed or refractory to standard treatments. AML, MDS that is very high- or high-risk as defined by the IPSS-R, and Philadelphia chromosome positive malignancies are excluded. * Upon discussion with the sponsor, other relapsed or refractory, potentially avapritinib-responsive hematologic neoplasms (e.g., evidence of aberrant KIT or platelet derived growth factor receptor (PDGFR) signaling) may be considered for enrollment. For Part 2, patients must have one of the following diagnoses, based on WHO diagnostic criteria: * ASM. * SM-AHN. The AHN must be myeloid, with the following exceptions that are excluded: AML, MDS that is very high- or high-risk as defined by the IPSS-R, and Philadelphia chromosome positive malignancies. * MCL. For Part 2,…