A Vaccine (STEMVAC) With Standard Endocrine-Based Therapy or Chemotherapy for the Treatment of Metastatic Hormone Receptor Positive, HER2 Negative Breast Cancer
A Phase II Study of STEMVAC Vaccine Therapy for Patients With Hormone Receptor Positive Metastatic Breast Cancer
3 other identifiers
interventional
40
1 country
1
Brief Summary
This phase II trial studies how well a vaccine, STEMVAC, works in combination with standard endocrine-based therapy (ET) with a CDK4/6 targeted drug therapy, or with the chemotherapy drug capecitabine, in treating patients with hormone receptor (HR)-positive, HER2-negative breast cancer that has spread from where it first started (primary site) to other places in the body (metastatic). STEMVAC is designed to target proteins that cancer cells use when they become more aggressive and start to spread, and it is believed to work by boosting the immune system to recognize and destroy the invader tumor cells that are causing the disease. Standard ET is treatment that adds, blocks, or removes hormones in order to slow or stop the growth of cancer. Standard CDK4/6 inhibitors may stop the growth of tumor cells and may kill them by blocking some of the enzymes needed for cell growth. Capecitabine is in a class of medications called antimetabolites. It is taken up by tumor cells and breaks down into fluorouracil, a substance that kills tumor cells. Giving STEMVAC in combination with standard ET or chemotherapy may be an effective treatment for metastatic HR positive, HER2 negative breast cancer.
Trial Health
Trial Health Score
Automated assessment based on enrollment pace, timeline, and geographic reach
participants targeted
Target at P25-P50 for phase_2
Started Nov 2025
Typical duration for phase_2
1 active site
Health score is calculated from publicly available data and should be used for screening purposes only.
Trial Relationships
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Study Timeline
Key milestones and dates
First Submitted
Initial submission to the registry
July 18, 2025
CompletedFirst Posted
Study publicly available on registry
August 8, 2025
CompletedStudy Start
First participant enrolled
November 17, 2025
CompletedPrimary Completion
Last participant's last visit for primary outcome
July 31, 2028
ExpectedStudy Completion
Last participant's last visit for all outcomes
December 31, 2028
March 9, 2026
December 1, 2025
2.7 years
July 18, 2025
March 6, 2026
Conditions
Outcome Measures
Primary Outcomes (2)
Incidence of adverse events (AEs)
Safety and systemic toxicity will be determined by chemical and clinical parameters evaluated at various time points. Toxicity grading will be evaluated according to the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events version 6.0 and monitoring of AEs will be done per Food and Drug Administration and NCI guidelines. The type and grade of toxicities noted during the immunization regimen will be summarized. The duration of toxicities will also be summarized using descriptive statistics such as mean and standard deviation. All AEs noted by the investigator will be tabulated according to the affected body system. The frequency and severity of adverse events will be summarized with a proportion and a 95% confidence interval (CI).
Up to 3 years after completion of study treatment
Incidence of immunogenicity
Will be defined as the sum of the interferon gamma enzyme-linked immunosorbent spot of all STEMVAC antigens on blood samples collected pre-vaccine as compared to 1-month post dose #3 of the STEMVAC vaccine and again after 2 booster doses of STEMVAC vaccine. Both incidence and magnitude will be assessed. Immune responses will be summarized with mean and standard deviation or median and range (if skewness is observed) over time, the change over time will be summarized with graphs, and also analyzed using linear mixed-effects regression models with normalizing transformation if necessary.
Pre-vaccine up to after 2 booster doses of STEMVAC vaccine (Up to 40 weeks)
Secondary Outcomes (3)
Progression-free survival (PFS)
From the start of treatment to the worsening of cancer as determined by primary treating oncologist or death whichever occurs first, assessed up to 3 years after completion of study treatment
Circulating tumor DNA (ctDNA)
Up to 3 years after completion of study treatment
Elimination of cancer cells associated with epithelial to mesenchymal transformation (EMT)
Up to 3 years after completion of study treatment
Study Arms (2)
Cohort 1 (STEMVAC, ET + CDK4/6i)
EXPERIMENTALAfter completion of 2 cycles of SOC ET + CDK4/6i therapy, patients receive STEMVAC ID on the following schedule: 1) Three "priming" doses every 28 days; 2) Two "booster" doses at 6 and 9 months after "priming" dose #3; and 3) Additional "booster" doses every 6 months in the absence of disease progression or unacceptable toxicity. Patients also undergo CT or ultrasound-guided biopsies, as well as collection of blood samples and CT or PET scans throughout the trial.
Cohort 2 (STEMVAC, capecitabine)
EXPERIMENTALAfter completion of 1 cycle of SOC capecitabine treatment, patients receive STEMVAC ID on the following schedule: 1) Three "priming" doses every 28 days; 2) Two "booster" doses at 6 and 9 months after "priming" dose #3; and 3) Additional "booster" doses every 6 months in the absence of disease progression or unacceptable toxicity. Patients also undergo CT or ultrasound-guided biopsies, collection of blood samples, and FES PET scans, as well as CT or PET scans throughout the trial.
Interventions
Given ID
Given SOC capecitabine
Undergo CT or ultrasound-guided biopsies
Given SOC CDK4/6i
Given SOC CDK4/6i
Undergo FES PET
Given SOC ET
Undergo PET or FES PET
Undergo CT or ultrasound-guided biopsies
Undergo CT or ultrasound-guided biopsies
Undergo collection of blood samples
Eligibility Criteria
You may qualify if:
- Patients must be at least ≥ 18 years of age
- Histologically confirmed hormone receptor positive metastatic breast cancer: Tumors that are positive for estrogen receptor (ER) and/or progesterone receptor (PR)
- HER2-negative or HER2-low will be included and defined as:
- + HER2 expression by immunohistochemistry (IHC) OR
- Fluorescence in situ hybridization (FISH) negative OR
- HER2 2+ and FISH negative
- HER2 low per standard of care in breast cancer
- Patients should be receiving the following therapies to be eligible for the study:
- Cohort 1: First or second line of endocrine therapy in the metastatic setting, in combination with a CDK4/6 inhibitor. Patients must have completed at least 2 cycles of CDK4/6 inhibitor. Patients who have stopped endocrine therapy for intolerance but remain on abemaciclib monotherapy will be considered for enrollment at the PI's discretion
- Cohort 2: Progressed on endocrine-based therapies and after completion of at least 1 cycle of capecitabine
- Subjects with Eastern Cooperative Oncology Group (ECOG) Performance Status Score of 0 or 1
- Willing to undergo up to two serial biopsies while on study
- Have at least 1 site of disease confirmed by the treating oncologist that could be biopsied during treatment
- White blood cell (WBC) ≥ 2000/mm\^3 (within 28 days of receiving the study vaccine)
- Lymphocyte count ≥ 500/mm\^3 (within 28 days of receiving the study vaccine)
- +7 more criteria
You may not qualify if:
- Patients with any of the following cardiac conditions:
- Symptomatic restrictive cardiomyopathy
- Dilated cardiomyopathy
- Unstable angina within 4 months prior to enrollment
- New York Heart Association functional class III-IV heart failure on active treatment
- Symptomatic pericardial effusion
- Uncontrolled hypertension
- Uncontrolled cardiac arrhythmias
- Patients with any autoimmune disease/comorbidity that require chronic steroids or immunosuppressants
- A non-breast malignancy requiring radiation or systemic therapy within last 5 years
- Known hypersensitivity reaction to the granulocyte-macrophage colony-stimulating factor (GM-CSF) adjuvant; any known contra-indication to GM-CSF
- Pregnant or breast feeding
- Known history of human immunodeficiency virus (HIV) infection, hepatitis B (e.g., hepatitis B virus surface antigen \[HBsAg\] reactive), or hepatitis C (e.g., hepatitis C virus \[HCV\] ribonucleic acid \[RNA\] \[qualitative\] is detected)
- Major surgery within the 4 weeks prior to initiation of study vaccine
- Current use of immunosuppressive agents or systemic corticosteroids. Topical, ocular, intra-articular, intranasal, and inhalational corticosteroids (with minimal systemic absorption) are allowed. Patients who have received systemic corticosteroids ≤ 30 days prior to starting study drug will be excluded
- +5 more criteria
Contact the study team to confirm eligibility.
Sponsors & Collaborators
Study Sites (1)
Fred Hutch/University of Washington Cancer Consortium
Seattle, Washington, 98109, United States
MeSH Terms
Interventions
Intervention Hierarchy (Ancestors)
Study Officials
- PRINCIPAL INVESTIGATOR
Natasha Hunter, MD
Fred Hutch/University of Washington Cancer Consortium
Central Study Contacts
Study Design
- Study Type
- interventional
- Phase
- phase 2
- Allocation
- NON RANDOMIZED
- Masking
- NONE
- Purpose
- TREATMENT
- Intervention Model
- PARALLEL
- Sponsor Type
- OTHER
- Responsible Party
- SPONSOR
Study Record Dates
First Submitted
July 18, 2025
First Posted
August 8, 2025
Study Start
November 17, 2025
Primary Completion (Estimated)
July 31, 2028
Study Completion (Estimated)
December 31, 2028
Last Updated
March 9, 2026
Record last verified: 2025-12
Data Sharing
- IPD Sharing
- Will not share