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Recruiting Phase 2, Phase 3 NCT04910685

NCT04910685 (HARBOR) Study to Evaluate Efficacy and Safety of BLU-263 Versus Placebo in Patients With Indolent Systemic Mastocytosis

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Clinical Trial Summary
NCT ID NCT04910685
Status Recruiting
Phase Phase 2, Phase 3
Sponsor Blueprint Medicines Corporation
Condition Indolent Systemic Mastocytosis
Study Type INTERVENTIONAL
Enrollment 534 participants
Start Date 2021-11-30
Primary Completion 2032-09-30

Eligibility & Interventions

Sex All sexes
Min Age 18 Years
Max Age N/A
Study Type INTERVENTIONAL
Interventions
ElenestinibPlacebo

Eligibility Fast-Check

Enter your details for a quick preliminary check. This does not replace medical advice.

What to Expect as a Participant

You will actively receive the study intervention — which may be a drug, biologic, device, or procedure.

In Phase 2, researchers evaluate early signs of effectiveness. You may be randomized to receive the active treatment or a comparator. Monitoring continues closely.

This trial targets 534 participants in total. It began in 2021-11-30 with a primary completion date of 2032-09-30.

⚠ This information is for research awareness only. Always consult your physician before joining any clinical trial. Participation is voluntary and you may withdraw at any time.

Brief Summary

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. Participants enrolled in Part 2 will roll over onto Part 3 to receive treatment with elenestinib in an open-label fashion following completion of the earlier Part. Part K will enroll participants with ISM who have previously received an approved selective KIT inhibitor. The study also includes pharmacokinetic (PK) groups that will enroll participants with ISM.

Eligibility Criteria

Key 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 SSM, confirmed by Central Pathology Review of BM biopsy and central review of B- and C-findings by WHO diagnostic criteria. Part 2: -Participant has confirmed diagnosis of ISM, confirmed by Central Pathology Review Key Exclusion Criteria: * Participant has been diagnosed with any of the following WHO systemic mastocytosis (SM) sub-classifications: cutaneous mastocytosis only, SM with an associated hematologic neoplasm of non-MC lineage (SM-AHN), aggressive SM, mast cell leukemia, or mast cell sarcoma. * Participant has been diagnosed with another myeloproliferative disorder. * Participant has organ damage attributable to SM. * Participant has clinically significant, uncontrolled, cardiovascular disease * Participant has a QT interval corrected using Fridericia's formula (QTcF) \> \> 470 milliseconds (msec) (for females) or \> 450 msec (for males). * Participant has a history of a primary malignancy that has been diagnosed or required therapy within 3 years. The following prior malignancies are not exclusionary: completely resected basal cell and squamous cell skin cancer, curatively treated localized prostate cancer, and completely resected carcinoma in situ of any site. * Time since any cytoreductive therapy including masitinib and midostaurin should be at least 5 half-lives or 14 days (whichever is longer), and for cladribine, interferon alpha, pegylated interferon, or antibody therapy \< 28 days or 5 half-lives of the drug (whichever is longer), before beginning the screening period. * Participant has received radiotherapy or psoralen and ultraviolet A (PUVA) therapy \< 14 days before beginning the screening period. Other protocol-defined criteria apply.

Contact & Investigator

Central Contact

Blueprint Medicines

✉ medinfo@blueprintmedicines.com

📞 617-714-6707

Frequently Asked Questions

Who can join the NCT04910685 clinical trial?

This trial is open to participants of all sexes, aged 18 Years or older, studying Indolent Systemic Mastocytosis. Full inclusion and exclusion criteria are listed in the Eligibility Criteria section. Always confirm your eligibility with the research team before applying.

What phase is the NCT04910685 trial and what does that mean for participants?

Phase 2 trials evaluate whether the treatment shows signs of effectiveness while continuing to monitor safety. More participants are enrolled than in Phase 1 to help refine the treatment protocol.

Is NCT04910685 currently recruiting?

Yes, NCT04910685 is actively recruiting participants. Contact the research team at medinfo@blueprintmedicines.com for enrollment information.

Where is the NCT04910685 trial being conducted?

This trial is being conducted at Birmingham, United States, Los Angeles, United States, Palo Alto, United States, Aurora, United States and 11 additional locations.

Who is sponsoring the NCT04910685 clinical trial?

NCT04910685 is sponsored by Blueprint Medicines Corporation. The trial plans to enroll 534 participants.

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ClinicalMetric — Independent clinical trial intelligence platform. Not affiliated with NIH, ClinicalTrials.gov, the U.S. FDA, or any pharmaceutical company, hospital, or clinical research organization. Trial data is sourced from ClinicalTrials.gov for informational purposes only and does not constitute medical advice. Do not make any treatment, enrollment, or health decisions based solely on information found here — always consult a qualified healthcare professional. Full Disclaimer  ·  Last Reviewed: September 2026  ·  Data Methodology