NCT04910685 · Blueprint Medicines Corporation
(HARBOR) Study to Evaluate Efficacy and Safety of BLU-263 Versus Placebo in Patients With Indolent Systemic Mastocytosis
What this study is about
This is a randomly assigned, where neither patients nor doctors know which treatment is given, compared against an inactive treatment, Phase 2/3 study comparing the effectiveness and safety of elenestinib (BLU-263) + symptom directed therapy (SDT) with placebo + SDT in participants with indolent systemic mastocytosis (ISM) whose symptoms are not adequately controlled by SDT.
View original scientific description
This is a randomized, double-blind, placebo-controlled, Phase 2/3 study comparing the efficacy and safety of elenestinib (BLU-263) + symptom directed therapy (SDT) with placebo + SDT in participants with indolent systemic mastocytosis (ISM) whose symptoms are not adequately controlled by SDT. Parts 1 and 2 will enroll participants with ISM.
Interventions
DRUG
Elenestinib
Elenestinib oral tablet
DRUG
Placebo
Placebo oral tablet
Primary outcome measures
Part 1: Number of participants with Treatment-emergent Adverse Events (TEAEs)
Time frame: Up to 12 weeks
Part 1: Mean change from baseline in ISM-Symptom in Assessment Form (ISM-SAF) Total Symptom Score (TSS)
Time frame: Baseline, Week 13
Part 2: Mean change from baseline in ISM-SAF TSS
Time frame: Baseline, Week 49
Part 3: Number of participants with Adverse Events (AEs)
Time frame: Up to 5 years
Part 3: Change from baseline in ISM-SAF TSS
Time frame: Baseline up to 5 years
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
Inclusion criteria
- All Participants: -Participant must have an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 2. Part 1 and PK groups:
- Participant has confirmed diagnosis of ISM, confirmed by Central Pathology Review
- Participant must have failed to achieve adequate symptom control for 1 or more Baseline symptoms, as determined by the Investigator, with at least 2 of the following symptom-directed therapies administered: H1 blockers, H2 blockers, proton-pump inhibitors, leukotriene inhibitors, cromolyn sodium, corticosteroids, or omalizumab.
- Participants must have SDT for ISM symptom management stabilized for at least 14 days prior to starting screening procedures.
- For participants receiving corticosteroids, the dose must be ≤ 20 mg/day prednisone or equivalent, and the dose must be stable for ≥ 14 days. Part K: -Participant has confirmed diagnosis of ISM, confirmed by Central Pathology Review Part S: -Participant has confirmed diagnosis of
Where
- Birmingham, Alabama
- Los Angeles, California
- Palo Alto, California
- Aurora, Colorado
- Atlanta, Georgia
- Boston, Massachusetts
- Ann Arbor, Michigan
- Rochester, Minnesota
- Buffalo, New York
- New York, New York
- Durham, North Carolina
- Cincinnati, Ohio
And 2 more locations — see the full list below.
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Jun 25, 2026 · Source of record for eligibility and locations