Bezuclastinib

Maximum plasma concentration (Cmax)

Area under the plasma concentration-time curve (AUC)

Maximum plasma concentration (Cmax)

Area under the plasma concentration-time curve (AUC)

Time to maximum observed plasma concentration (Tmax)

Time from first dose to documented disease progression or death due to any cause, whichever occurs first

Area under the plasma concentration-time curve (AUC)

Maximum plasma concentration (Cmax)

mPFS will be summarized with a Kaplan-Meier curve

Selection of the recommended dose to be used in subsequent parts of the study.

Mean absolute change on the Mastocytosis Symptom Severity Daily Diary (MS2D2)

CTCAE v5

RP2D was determined by incidence of dose limiting toxicity (DLT) using Common Terminology Criteria for Adverse Events (CTCAE) V4.03. DLTs: AEs that occurred during Cycle 1, possibly/probably related to study drug, and met 1 of the following criteria: Hematologic Toxicities: Grade 4 neutropenia for \>7 days, Grade ≥3 neutropenia with fever, Grade 4 thrombocytopenia, Grade ≥3 thrombocytopenia for \>7 days, Grade 4 anemia; Other Toxicities: Any Grade ≥3 (AE or laboratory) toxicity despite adequate supportive care except for following: Grade ≥3 nausea, vomiting, or diarrhea that resolved to Grade ≤2 within 72 hours; Grade 3 fatigue that resolved to Grade ≤2 within 14 days; Grade ≥3 asymptomatic changes in alkaline phosphatase, hypomagnesemia, hyperglycemia, or hypophosphatemia; Grade 3 increases in transaminases for ≤5 days; Any other Grade ≥3 toxicity for which further dose escalation deemed inappropriate.

An adverse event (AE) was any untoward medical occurrence in a participant administered study drug, which did not necessarily have a causal relationship with the treatment. An AE could be any unfavorable and unintended sign (for example, including an abnormal laboratory finding), symptom, or disease temporally associated with the use of the study drug, whether or not it was considered to be study drug related. This included any newly occurring event or previous condition that had increased in severity or frequency since the administration of study drug. A treatment-emergent AE (TEAE) was an AE that started or worsened in severity on or after the date of the initial dose of study drug. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.

AUC0-24 was determined by the linear trapezoidal rule for the ascending portion and by the log trapezoidal rule for the descending portion of the plasma profile. For BID dosing, Cycle 1 Day 15 AUC0-24 was calculated as 2 x area under the concentration time curve from time zero to 12 hours after dosing (AUC0-12). Missing concentration data were excluded from Pharmacokinetic (PK) analysis.

Cmax was taken directly from bioanalytical data.

Tmax was taken directly from merged clinical and bioanalytical data, with time presented as nominal time relative to dose.

Participants in a selected Part 1 cohort (350 mg QD) participated in a PK substudy to obtain more complete information on the PK profile of PLX9486. Participants received a single dose of 350 mg of PLX9486 10 days prior to the start of repeated QD dosing and plasma concentrations were followed 0.5, 1, 2, 4, 6, and 9 hours postdose, and then once daily for 9 additional days prior to Cycle 1 Day 1.

RP2D was determined by incidence of DLT using CTCAE version 4.03 for severity grade. DLTs were defined as AEs that occurred during Cycle 1, classified as possibly/probably related to study drug, and met 1 of the following criteria: Hematologic Toxicities: Grade 4 neutropenia for \>7 days, Grade ≥3 neutropenia with fever, Grade 4 thrombocytopenia, Grade ≥3 thrombocytopenia for \>7 days or with bleeding, Grade 4 anemia; Other Toxicities: Any Grade ≥3 (AE or laboratory) toxicity despite adequate supportive care except for the following: Grade ≥3 nausea, vomiting, or diarrhea that resolved to Grade ≤2 within 72 hours; Grade 3 fatigue that resolved to Grade ≤2 within 14 days; Grade ≥3 asymptomatic changes in alkaline phosphatase, hypomagnesemia, hyperglycemia, or hypophosphatemia; Grade 3 increases in transaminases for ≤5 days; Any other Grade ≥3 toxicity for which further dose escalation deemed inappropriate.

RP2D was determined by incidence of DLT using CTCAE version 4.03 for severity grade. DLTs were defined as AEs that occurred during Cycle 1, classified as possibly/probably related to study drug, and met 1 of the following criteria: Hematologic Toxicities: Grade 4 neutropenia for \>7 days, Grade ≥3 neutropenia with fever, Grade 4 thrombocytopenia, Grade ≥3 thrombocytopenia for \>7 days or with bleeding, Grade 4 anemia; Other Toxicities: Any Grade ≥3 (AE or laboratory) toxicity despite adequate supportive care except for the following: Grade ≥3 nausea, vomiting, or diarrhea that resolved to Grade ≤2 within 72 hours; Grade 3 fatigue that resolved to Grade ≤2 within 14 days; Grade ≥3 asymptomatic changes in alkaline phosphatase, hypomagnesemia, hyperglycemia, or hypophosphatemia; Grade 3 increases in transaminases for ≤5 days; Any other Grade ≥3 toxicity for which further dose escalation deemed inappropriate.

An AE was any untoward medical occurrence in a participant administered study drug, which did not necessarily have a causal relationship with the treatment. An AE could be any unfavorable and unintended sign (for example, including an abnormal laboratory finding), symptom, or disease temporally associated with the use of the study drug, whether or not it was considered to be study drug related. This included any newly occurring event or previous condition that had increased in severity or frequency since the administration of study drug. A TEAE was an AE that started or worsened in severity on or after the date of the initial dose of study drug. Treatment-related TEAEs included all events reported as "possibly related" or "probably related" to any of study treatment. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.

An AE was any untoward medical occurrence in a participant administered study drug, which did not necessarily have a causal relationship with the treatment. An AE could be any unfavorable and unintended sign (for example, including an abnormal laboratory finding), symptom, or disease temporally associated with the use of the study drug, whether or not it was considered to be study drug related. This included any newly occurring event or previous condition that had increased in severity or frequency since the administration of study drug. A TEAE was an AE that started or worsened in severity on or after the date of the initial dose of study drug. Treatment-related TEAEs included all events reported as "possibly related" or "probably related" to any of study treatment. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.