Open-Label Extension Study of Marstacimab in Hemophilia Participants With or Without Inhibitors

AN OPEN-LABEL EXTENSION STUDY TO EVALUATE THE LONG-TERM SAFETY, TOLERABILITY, AND EFFICACY OF MARSTACIMAB PROPHYLAXIS IN SEVERE (COAGULATION FACTOR ACTIVITY <1%) HEMOPHILIA A PARTICIPANTS WITH OR WITHOUT INHIBITORS OR MODERATELY SEVERE TO SEVERE HEMOPHILIA B PARTICIPANTS (COAGULATION FACTOR ACTIVITY ≤2%) WITH OR WITHOUT INHIBITORS

Study B7841007 is an open-label extension study to assess the long-term safety, tolerability, and efficacy of prophylaxis treatment with marstacimab in participants who did not require "Early Termination" from the Phase 3 Study B7841005 and from the Phase 3 Study B7841008.

Study B7841005: approximately 145 adolescent and adult participants 12 to <75 years of age with severe hemophilia A or moderately severe to severe hemophilia B (defined as FVIII activity <1% or FIX activity ≤2%, respectively) with or without inhibitors are expected to be enrolled in Study B7841005 during which they will receive prophylaxis (defined as treatment by SC injection of marstacimab).

Study B7841008: this is an ongoing Phase 3, open-label study in pediatric participants <18 years of age with severe hemophilia A (FVIII Coagulation Factor Activity <1%) or moderately severe to severe hemophilia B (FIX Coagulation Factor Activity ≤2%). A sequential approach will be used in enrolling at least 100 pediatric participants, at least 20 of which will be aged ≥12 to <18 years and at least 80 participants will be aged ≥1 to <12 years. At the start of study B7841008, the dosing and data available in adolescent and adult participants in Study B7841005 supported the initiation of B7841008 study in participants aged ≥12 to <18 years. Subsequently, additional safety and efficacy data from adolescent participants in Study B7841005 became available for benefit/risk assessment in support of dosing participants aged ≥6 to <12 years. Based on the positive benefit/risk assessment conducted by both internal Pfizer review and eDMC review, dosing of the ≥6 to <12 years age group was initiated in June 2023 in B7841008 Study. Data from participants ≥6 years from B7841008 Study and Study B7841005 will support the dosing of participants aged ≥1 to <6 years.

All participants will be provided the prefilled pen (PFP) for administration of marstacimab in the study. Use of the prefilled syringe (PFS) will be permitted at the investigator's discretion for those participants who have difficulty with administration of the PFP. Additionally, participants will be provided the PFS for use in this study in countries where the PFS is anticipated to be the only presentation available commercially. An optional, open-label, single arm, substudy using the PFP was completed in the first 23 participants rolled over from Study B7841005 who agreed to participate in the substudy.

Study Overview

• Status: Recruiting
• Conditions: Hemophilia A; Hemophilia B
• Intervention / Treatment: Drug: PF-06741086

• Study Type: Interventional
• Enrollment (Estimated): 245
• Phase: Phase 3

Contacts and Locations

• Study Contact: Name: Pfizer CT.gov Call Center; Phone Number: 1-800-718-1021; Email: ClinicalTrials.gov_Inquiries@pfizer.com

Study Locations

• Argentina
  • Mendoza, Argentina, M5501
    • Recruiting
    • Arbesu Hematología
• Australia
  • Victoria
    • Melbourne, Victoria, Australia, 3052
      • Recruiting
      • Royal Children's Hospital
• Brazil
  • Espírito Santo
    • Vitória, Espírito Santo, Brazil, 29047-105
      • Recruiting
      • HEMOES
• Canada
  • Alberta
    • Edmonton, Alberta, Canada, T6G 2B7
      • Recruiting
      • Stollery Children's Hospital
  • Ontario
    • Hamilton, Ontario, Canada, L8N3Z5
      • Recruiting
      • Hamilton Health Sciences - McMaster University Medical Centre
    • Hamilton, Ontario, Canada, L8N 3Z5
      • Recruiting
      • Hamilton Health Sciences - McMaster University Medical Centre
• China
  • Beijing, China, 100045
    • Recruiting
    • Beijing Children's Hospital, Capital Medical University
  • Guangdong
    • Guangzhou, Guangdong, China, 510515
      • Recruiting
      • Nanfang Hospital, Southern Medical University
  • Guizhou
    • Guiyang, Guizhou, China, 550004
      • Recruiting
      • The Affiliated Hospital of Guizhou Medical University
  • Hubei
    • Wuhan, Hubei, China, 430030
      • Recruiting
      • Tongji Hospital, Tongji Medical College of Huazhong University of Science and Technology
  • Jiangxi
    • Nanchang, Jiangxi, China, 330006
      • Recruiting
      • Jiangxi Provincial People's Hospital
    • Nanchang, Jiangxi, China, 330038
      • Recruiting
      • Jiangxi Provincial People's Hospital
  • Tianjin Municipality
    • Tianjin, Tianjin Municipality, China
      • Recruiting
      • Institute of hematology&blood disease hospital
• Croatia
  • Zagreb, Croatia, 10000
    • Active, not recruiting
    • Klinicki bolnicki centar Zagreb
• Denmark
  • Central Jutland
    • Aarhus, Central Jutland, Denmark, 8200
      • Recruiting
      • Aarhus Universitetshospital, Skejby
• France
  • Paris, France, 75015
    • Recruiting
    • Hôpital Universitaire Necker Enfants Malades
• Hong Kong
  • Hong Kong, Hong Kong
    • Recruiting
    • Queen Mary Hospital
  • Hong Kong, Hong Kong
    • Recruiting
    • Prince of Wales Hospital
  • Hong Kong, Hong Kong, 999077
    • Recruiting
    • The University of Hong Kong (HKU)-Queen Mary Hospital (QMH)
  • Ma Liu Shui, Hong Kong
    • Recruiting
    • The Chinese University of Hong Kong
• India
  • Gjuarat
    • Surat, Gjuarat, India, 395002
      • Recruiting
      • Nirmal Hospital Pvt Ltd.
  • Maharashtra
    • Mumbai, Maharashtra, India, 400022
      • Recruiting
      • K.J Somaiya Hospital & Research Centre, Somaiya Ayurvihar Complex
    • Pune, Maharashtra, India, 411004
      • Recruiting
      • Sahyadri Super Speciality Hospital
  • West Bengal
    • Kolkata, West Bengal, India, 700014
      • Recruiting
      • Nil Ratan Sircar Medical College and Hospital
• Israel
  • Central District
    • Ramat Gan, Central District, Israel, 5262100
      • Recruiting
      • Sheba Medical Center
• Italy
  • Milan, Italy, 20122
    • Recruiting
    • Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico
  • Milan, Italy, 20122
    • Recruiting
    • Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico
  • Liguria
    • Genoa, Liguria, Italy, 16147
      • Recruiting
      • IRCCS Istituto Giannina Gaslini
  • Milano
    • Rozzano, Milano, Italy, 20089
      • Recruiting
      • Istituto Clinico Humanitas
  • RM
    • Roma, RM, Italy, 00161
      • Recruiting
      • AOU Policlinico Umberto I
• Japan
  • Hiroshima, Japan, 734-8551
    • Recruiting
    • Hiroshima University Hospital
  • Saga, Japan, 849-8501
    • Recruiting
    • Saga University Hospital
  • Aichi-ken
    • Nagoya, Aichi-ken, Japan, 466-8560
      • Recruiting
      • Nagoya University Hospital - Transfusion Medicine
  • Nagano
    • Azumino, Nagano, Japan, 399-8288
      • Recruiting
      • Nagano Children's Hospital
  • Nara
    • Kashihara, Nara, Japan, 634-0813
      • Recruiting
      • Nara Medical University Hospital
  • Saitama
    • Lruma-gun, Saitama, Japan, 350-0495
      • Recruiting
      • Saitama Medical University Hospital
    • Saitama-shi, Saitama, Japan, 330-8777
      • Recruiting
      • Saitama Children's Medical Center
• Mexico
  • Yucatán
    • Mérida, Yucatán, Mexico, 97130
      • Recruiting
      • Centro Multidisciplinario para el Desarrollo Especializado de la Investigacion Clinica en Yucatán S.
• Oman
  • Muscat, Oman, 123
    • Recruiting
    • Sultan Qaboos University Hospital
• Serbia
  • Belgrade, Serbia, 11000
    • Recruiting
    • Institute for Mother and Child healthcare "Dr Vukan Cupic"
  • Niš, Serbia, 18000
    • Recruiting
    • Clinical Center Nis
• Slovakia
  • Košice, Slovakia, 040 11
    • Recruiting
    • Detska fakultna nemocnica Kosice
  • Martin, Slovakia, 036 59
    • Recruiting
    • Univerzitná nemocnica Martin
• South Africa
  • Gauteng
    • Benoni, Gauteng, South Africa, 1500
      • Active, not recruiting
      • Worthwhile Clinical Trials
    • Johannesburg, Gauteng, South Africa, 2193
      • Active, not recruiting
      • Charlotte Maxeke Johannesburg Academic Hospital
    • Johannesburg, Gauteng, South Africa, 2193
      • Active, not recruiting
      • Wits Health Consortium
• South Korea
  • Seoul-teukbyeolsi [seoul]
    • Seoul, Seoul-teukbyeolsi [seoul], South Korea, 05278
      • Recruiting
      • Kyung Hee University Hospital at Gangdong
  • Seoul-teukbyeolsi[seoul]
    • Seoul, Seoul-teukbyeolsi[seoul], South Korea, 03722
      • Recruiting
      • Severance Hospital, Yonsei University Health System
  • Taegu-kwangyǒkshi
    • Daegu, Taegu-kwangyǒkshi, South Korea, 41944
      • Recruiting
      • Kyungpook National University Hospital
• Spain
  • A Coruña, Spain, 15006
    • Recruiting
    • Hospital Universitario A Coruna
  • Barcelona, Spain, 08035
    • Recruiting
    • Hospital Universitario Vall d´Hebron
  • Madrid, Spain, 28046
    • Recruiting
    • Hospital Universitario La Paz
  • Zaragoza, Spain, 50009
    • Recruiting
    • Hospital Universitario Miguel Servet
• Taiwan
  • Taichung, Taiwan, 407219
    • Recruiting
    • Taichung Veterans General Hospital
  • Changhua County
    • Changhua, Changhua County, Taiwan, 500
      • Recruiting
      • Changhua Christian Hospital
• Turkey (Türkiye)
  • Adana, Turkey (Türkiye), 01130
    • Recruiting
    • Acibadem Adana Hospital
  • Ankara, Turkey (Türkiye), 06560
    • Recruiting
    • Gazi University Health Research and Application Center Gazi Hospital
  • Ankara, Turkey (Türkiye), 06500
    • Recruiting
    • Gazi University Medical Faculty
  • Ankara, Turkey (Türkiye), 06100
    • Recruiting
    • Hacettepe University Faculty of Medicine
  • Ankara, Turkey (Türkiye), 06230
    • Recruiting
    • Hacettepe University Medical Faculty Hospital
  • Gaziantep, Turkey (Türkiye), 27310
    • Recruiting
    • Gaziantep University Şahinbey Research and Practice Hospital
  • Istanbul, Turkey (Türkiye), 34093
    • Recruiting
    • Istanbul University Oncology Institute
  • Istanbul, Turkey (Türkiye), 34452
    • Recruiting
    • Istanbul Universitesi Klinik Arastirmalar Mukemmeliyet Uygulama ve Arastirma Merkezi
  • Izmir, Turkey (Türkiye), 35100
    • Recruiting
    • Ege University Faculty of Medicine
  • Izmir, Turkey (Türkiye), 35040
    • Recruiting
    • Ege University Faculty of Medicine
  • Kayseri, Turkey (Türkiye), 38039
    • Recruiting
    • Erciyes University Faculty of Medicine
  • Samsun, Turkey (Türkiye), 55200
    • Recruiting
    • Ondokuz Mayıs University Healthcare Practice and Research Center
  • Samsun, Turkey (Türkiye), 55280
    • Recruiting
    • Ondokuz Mayıs University Medical Faculty Local Laboratory
• United Kingdom
  • London, United Kingdom, SE1 7EH
    • Recruiting
    • Guy's & St Thomas' NHS Foundation Trust, St Thomas' Hospital
  • England
    • Newcastle upon Tyne, England, United Kingdom, NE1 4LP
      • Recruiting
      • Royal Victoria Infirmary
  • London, CITY of
    • London, London, CITY of, United Kingdom, SE1 9RT
      • Recruiting
      • Guy's & St Thomas' NHS Foundation Trust
• United States
  • Iowa
    • Iowa City, Iowa, United States, 52242
      • Active, not recruiting
      • University of Iowa
  • New York
    • New Hyde Park, New York, United States, 11040
      • Recruiting
      • Northwell Health HTC
  • Pennsylvania
    • Philadelphia, Pennsylvania, United States, 19195
      • Recruiting
      • The Feinstein Institutes for Medical Research
  • Washington
    • Seattle, Washington, United States, 98101
      • Recruiting
      • Washington Institute for Coagulation d/b/a WACBD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 12 years to 74 years (Child, Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• All participants will have a minimum body weight as defined by parent studies
• Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, and other study procedures.
• Participants have successfully completed participation in parent studies, defined as did not require "Early Termination"

Exclusion Criteria:

• Previous or current treatment for or history of coronary artery disease, venous or arterial thrombosis (CTCAE Grade >3), or ischemic disease (except catheter-associated thrombosis)
• Abnormal renal function as defined by eGFR <30 mL.min/1.73 m(2)
• Known planned surgical procedure during the planned study period
• Unstable hepatic function as determined by the Investigator clinical assessment and review of the participant's most recent laboratory results, which would make the participant inappropriate for the study
• For participants known to be HIV+, worsening disease status as determined by the Investigator clinical assessment and review of participant's most recent laboratory results, to include recent locally available CD4 count (if available), which would make the participant inappropriate for the study
• Regular, concomitant therapy with immunomodulatory drugs (eg, IVIG, and routine systemic corticosteroids, rituximab)
• Ongoing or planned use of immune tolerance induction or prophylaxis with FVIII or FIX replacement during the study
• Participation in other study involving investigational drug(s) or investigational vaccine(s) within 30 days or 5 half-lives prior to or during study participation, with the exception of participation in parent studies
• Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the Investigator, and their respective family members

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: PF-06741086; For participants aged ≥12 years 300 milligrams(mg) subcutaneous (sc) loading dose followed by 150 mg sq once weekly (qw). 300 mg sc qw is prescribed for participants who meet dose escalation criteria. For participants aged ≥6 to <12 years is marstacimab 150 mg SC for initial loading dose followed by 75 mg SC QW. 150 mg sc qw is prescribed for participants who meet dose escalation criteria.

Drug: PF-06741086; For participants aged ≥12 years 300 milligrams(mg) subcutaneous (sc) loading dose followed by 150 mg sq once weekly (qw). 300 mg sc qw is prescribed for participants who meet dose escalation criteria. For participants aged ≥6 to <12 years is marstacimab 150 mg SC for initial loading dose followed by 75 mg SC QW. 150 mg sc qw is prescribed for participants who meet dose escalation criteria.; Other Names: marstacimab

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Number of subject reporting Adverse Events	Baseline up to 7 years
Number of subjects reporting Serious Adverse Events	Baseline up to 7 years
Incidence and severity of thrombotic events	Baseline up to 7 years
Incidence and severity of thrombotic microangiopathy	Baseline up to 7 years
Number of subjects reporting Disseminated intravascular coagulalopathy/consumption coagulopathy	Baseline up to 7 years
Incidence of clinically significant persistent NAb against marstacimab	Baseline up to 7 years
Incidence and severity of injection site reaction	Baseline up to 7 years
Clinically significant changes in vital signs from baseline	Baseline up to 7 years
Incidence of clinically significant laboratory value abnormalities	Baseline up to 7 years
Incidence of severe hypersensitivity and anaphylactic reactions	Baseline up to 7 years

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Annualized rate of bleeding episodes	Derived for each subject for each treatment period by using the following formula: ABR = number of bleeds requiring treatments/ (days on treatment period / 365.25)	Baseline up to 7 years
Total coagulation factor product consumption		Baseline up to 7 years
Incidence of joint bleeds		Baseline up to 7 years
Incidence of spontaneous bleeds		Baseline up to 7 years
Incidence of target joint bleeds		Baseline up to 7 years
Incidence of total bleeds (treated and untreated)		Baseline up to 7 year
Change in number of target joints per subject from baseline		Baseline up to 7 years
Changes in Health Utilities Measure questionnaire data		Baseline up to 7 years
Changes in Haem-A-QoL questionnaire data for participants ≥17 years of age		Baseline up to 7 years
Total bypass product consumption		Baseline up to 7 years
Change in joints measured by the HJHS	Change in joints as measured by the HJHS for participants ≥4 years of age	Baseline up to 7 years
Changes in Haemo-QoL questionnaire data	Haemo-QoL CII (Ages 8 to <12 years), Haemo-QoL (Ages 12 to <17),	Baseline up to 7 years
Changes in EQ-5D questionnaire data	EQ-5D-Y Proxy (Ages ≥ 4 to ≤ 6 years), EQ-5D-Y Self (Ages ≥ 7 to ≤ 11 years), EQ-5D-5L (Ages ≥12)	Baseline up to 7 years

Collaborators and Investigators

• Sponsor: Pfizer
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): November 17, 2021
• Primary Completion (Estimated): July 31, 2030
• Study Completion (Estimated): July 31, 2030

Study Registration Dates

• First Submitted: November 11, 2021
• First Submitted That Met QC Criteria: December 1, 2021
• First Posted (Actual): December 6, 2021

Study Record Updates

• Last Update Posted (Actual): April 14, 2026
• Last Update Submitted That Met QC Criteria: April 9, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: Factor VIII Inhibitor; Factor IX Inhibitor; PF-06741086; Marstacimab; Anti-TFPI
• Additional Relevant MeSH Terms: Genetic Diseases, Inborn; Hematologic Diseases; Blood Coagulation Disorders; Hemorrhagic Disorders; Genetic Diseases, X-Linked; Blood Coagulation Disorders, Inherited; Coagulation Protein Disorders; Congenital, Hereditary, and Neonatal Diseases and Abnormalities; Hemic and Lymphatic Diseases; Hemophilia A; Hemophilia B; marstacimab
• Other Study ID Numbers: B7841007; PHASE 3 ANTI-TFPI OLE (Other Identifier: Alias Study Number); 2022-500470-33-00 (Registry Identifier: CTIS (EU))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No