RECRUITING Phase 2 / Phase 3 ClinicalTrials.gov

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

Sponsor: Blueprint Medicines Corporation • ClinicalTrials.gov ID: NCT04910685

Registry updated: 2026-10-07

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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. 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.

Interventions

Elenestinib (Drug)
Elenestinib oral tablet
Placebo (Drug)
Placebo oral tablet

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.

Conditions

Indolent Systemic Mastocytosis Smoldering Systemic Mastocytosis

Locations

University of Alabama at Birmingham — Birmingham, Alabama, United States
Orso Health, Modena Allergy and Asthma Inc — La Jolla, California, United States
David Geffen School of Medicine at UCLA — Los Angeles, California, United States
Stanford Cancer Institute — Palo Alto, California, United States
UCHealth Blood Disorders and Cell Therapies Center - Anschutz Medical Campus — Aurora, Colorado, United States
Winship Cancer Institute, Emory University — Atlanta, Georgia, United States
Brigham and Women's Hospital — Boston, Massachusetts, United States
Michigan Medicine University of Michigan — Ann Arbor, Michigan, United States
Mayo Clinic — Rochester, Minnesota, United States
Roswell Park Cancer Institute — Buffalo, New York, United States
Columbia University Medical Center — New York, New York, United States
Duke Asthma, Allergy and Airway Center — Durham, North Carolina, United States
University of Cincinnati Medical Center — Cincinnati, Ohio, United States
The University of Texas, MD Anderson Cancer Center — Houston, Texas, United States
Huntsman Cancer Institute, University of Utah — Salt Lake City, Utah, United States
CHP Centro Hematologico Pavlovsky — Buenos Aires, Argentina
Consultorios Medicos Dr. Doreski - Fundacion Respirar — Buenos Aires, Argentina
Princess Alexandra Hospital — Woolloongabba, Queensland, Australia
The Alfred Hospital — Melbourne, Victoria, Australia
The Canberra Hospital — Garran, Australia
Kepler Universitatsklinikum, Med Campus III. Clinic of Internal Medicine 3 - Hematology and Oncology — Linz, Austria
Unitversitair Ziekenhuis Antwerpen — Edegem, Antwerpen, Belgium
Universitair Ziekenhuis Gent — Ghent, Belgium
CHU Tivoli — La Louvière, Belgium
UZ Leuven — Leuven, Belgium
Hospital das Clínicas da Faculdade de Medicina da USP - HCFMUSP — São Paulo, Brazil
Clinica Alemana de Santiago — Santiago, Chile
Fundación Valle del Lili — Cali, Colombia
Fakultní nemocnice Brno, Interní hematologická a onkologická klinika — Brno, Czechia
Fakultní nemocnice Královské Vinohrady, Hematologická klinika 3. LF UK v Praze a FNKV — Prague, Czechia
Odense University Hospital and University of Southern Denmark — Odense, Denmark
CHU Amiens-Picardie — Amiens, France
CHU de Caen — Caen, France
CHU Grenoble — Grenoble, France
CHU de Limoges — Limoges, France
CHU de Nantes — Nantes, France
Hôpital de la Pitié Salpétrière — Paris, France
Hôpital Necker - Départementd 'HématologieA dultes — Paris, France
CHU de Poitiers — Poitiers, France
CHU Toulouse - Hopital Larrey — Toulouse, France
Universitätsklinikum RWTH Aachen Klinik für Hämatologie, Onkologie, Hämostaseologie und Stammzelltransplantation — Aachen, Germany
Charité - Universitätsmedizin Berlin Institute of Allergology — Berlin, Germany
University Clinic Erlangen — Erlangen, Germany
University Clinic Hamburg Eppendorf — Hamburg, Germany
Universitatsklinikum Schleswig-Holstein, Campus Lubeck — Lübeck, Germany
Universitätsmedizin Mannheim III. Medizinische Klinik Universität Heidelberg Medizinische Fakultät Mannheim — Mannheim, Germany
LMU Klinikum — Munich, Germany
Klinikum rechts der Isar der Technischen Universitaet Muenchen — München, Germany
University General Hospital - General Hospital of West Attica — Chaïdári, Greece
General Hospital of Thessaloniki "G. Papanikolaou" — Thessaloniki, Greece
Cork University Hospital — Cork, Ireland
UOC Ematologia — Milan, Lombardy, Italy
SOD Ematologia (Ambulatori)- AOUC Azienda Ospedaliero Universitaria Careggi — Florence, Tuscany, Italy
Unita Operativa di Ematologia AOU Policlinico S. Orsola-Malpighi — Bologna, Italy
AOU Policlinico G.Rodolico - San Marco — Catania, Italy
Fondazione IRCCS Cà Granda Ospedale Maggiore Policlinico — Milan, Italy
S.C. Ematologia Fondazione I.R.C.C.S. Policlinico San Matteo — Pavia, Italy
S.S.D. Immunologia Clinica e Allergologia Azienda Ospedaliera Universitaria San Giovanni di Dio e Ruggi d'Aragona — Salerno, Italy
Unità Operativa di Allergologia Azienda Ospedaliera Universitaria Integrata di Verona — Verona, Italy
Azienda Unita Locale Socia Sanitaria N8 Berica — Vicenza, Italy
ErasmusMC — Rotterdam, South Holland, Netherlands
University Medical Center Groningen — Groningen, Netherlands
Maastricht UMC+ — Maastricht, Netherlands
Oslo University Hospital — Oslo, Norway
Uniwersyteckie Centrum Kliniczne Klinika Alergologii — Gdansk, Poland
Samodzielny Publiczny Za kład Opieki Zdrowotnej Szpital Uniwersytecki w Krakowie — Krakow, Poland
Centro Hospitalar de Lisboa Central, E.P.E. - Hospital de Santo Antonio dos Capuchos — Lisbon, Portugal
CHUPorto, EPE - Hospital de Santo António — Porto, Portugal
Centro Hospitalar Universitario Sao Joao, E.P.E. — Porto, Portugal
Unidade Local de Saude de Matosinhos, EPE - Hospital Pedro Hispanc — Senhora Da Hor, Portugal
Spitalul Clinic Colentina Bucuresti — Bucharest, Romania
Spitalul Universitar De Urgenta Bucuresti — Bucharest, Romania
Hospital Universitario Vall d'Hebron — Barcelona, Spain
Hospital Universitario Ramon y Cajal — Madrid, Spain
Hospital Virgen del Valle - Instituto de Estudios de Mastocitosis de Castilla-La Mancha — Toledo, Spain
Karolinska Universitetssjukhuset Huddinge — Stockholm, Sweden
Uppsala University Hospital — Uppsala, Sweden
University Hospital Basel — Basel, Switzerland
Luzerner Kantonsspital — Lucerne, Switzerland
Ankara Universitesi Tip Fakultesi Cebeci Hastanesi — Ankara, Turkey (Türkiye)
lstanbul Universitesi lstanbul Tip Fakultesi Hastanesi — Istanbul, Turkey (Türkiye)
Mersin VM Medikal Park Hastanesi — Mersin, Turkey (Türkiye)
University Hospital of Wales — Cardiff, Wales, United Kingdom
Queen Elizabeth Hospital, University Hospital Birmingham — Birmingham, United Kingdom
University College London Hospitals (UCLH), Haematology Cancer Clinical Trials Unit — London, United Kingdom
Guy's and St Thomas's NHS Foundation Trust — London, United Kingdom
GenesisCare — Oxford, United Kingdom
University Hospital Plymouth Trust - Derriford Hospital — Plymouth, United Kingdom

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Data sourced from ClinicalTrials.gov, a service of the U.S. National Institutes of Health.

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