FLASH-Breast: Evaluating the Efficacy of Fezolinetant in Reducing Vasomotor Symptoms in Women With Breast Cancer on Endocrine Therapy

May 30, 2026 updated by: Maryam Lustberg, Yale University

A Randomized Phase II Study to Evaluate the Efficacy of Fezolinetant in Reducing Vasomotor Symptoms in Women With Breast Cancer on Endocrine Therapy

This is a phase II, randomized, double-blinded, placebo-controlled trial designed to evaluate the efficacy of fezolinetant (45 mg a day) vs. placebo in reducing moderate to severe vasomotor symptoms (VMS) in breast cancer survivors on endocrine therapy (tamoxifen, aromatase inhibitors). The trial will proceed in a single stage, and the total of 92 participants will be randomized in 1:1 fashion to fezolinetant or placebo arm respectively.

Study Overview

Detailed Description

This is a phase II, randomized, double-blinded, placebo-controlled trial designed to evaluate the efficacy of fezolinetant (45 mg a day) vs. placebo in reducing moderate to severe vasomotor symptoms (VMS) in breast cancer survivors on endocrine therapy (tamoxifen, aromatase inhibitors). The trial will proceed in a single stage, and the total of 92 participants will be randomized in 1:1 fashion to fezolinetant or placebo arm respectively. After the 7-14-day screening period when all the baseline, pre-treatment measures will be collected, we will record daily data on frequency and severity of VMS and calculate weekly averages of both metrics. After the 12 weeks treatment period, formal efficacy analysis will be conducted and the treatment with fezolinetant will be deemed efficacious if the final weekly average of daily frequency of VMS will be significantly reduced compared to the 'week12 - baseline' difference of the placebo arm. Upon conclusion of the formal 12-week treatment assignment, once VMS final assessment has been recorded, we will unblind the study participants to their treatment assignment. Participants will be then allowed to cross over shall they choose to do so. Due to the vast availability of safety and efficacy data in general population, we did not include interim efficacy/futility or safety analysis.

Our hypothesis is that neurokinin blockade by fezolinetant will significantly reduce vasomotor symptoms in breast cancer survivors on endocrine therapy (tamoxifen or aromatase-inhibitor) measured by mean change in frequency of moderate to severe VMS based on patient-reported data from baseline to 12-weeks.

Study Type

Interventional

Enrollment (Estimated)

92

Phase

  • Phase 2

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

    • Connecticut
      • New Haven, Connecticut, United States, 06511
        • Recruiting
        • Yale University
        • Principal Investigator:
          • Maryam Lustberg, MD
        • Contact:
    • Ohio
      • Columbus, Ohio, United States, 43201
        • Not yet recruiting
        • The Ohio State University Comprehensive Cancer Center
        • Principal Investigator:
          • Sagar Sardesai, MD
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

Women with diagnosed, histologically confirmed, clinical stage I-III, HR+ invasive breast cancer as defined by ASCO CAP guidelines for whom adjuvant endocrine therapy would be indicated, regardless of HER2 status.

Age 18 years and older.

Currently on endocrine therapy (tamoxifen or aromatase inhibitors) as part of standard of care treatment for HR+ breast cancer. Endocrine therapy may be administered with or without ovarian suppression and/or CDK4/6 inhibitors as permitted in Section 7.1.1. Participants with HER2-positive disease are eligible and may receive concurrent HER2 monoclonal antibody therapy (e.g., trastuzumab or pertuzumab), but not HER2 antibody-drug conjugates (e.g., ado-trastuzumab emtansine T-DM1, or trastuzumab deruxtecan T-DXd).

Willing and able to provide written informed consent/assent for the trial.

Postmenopausal as defined by spontaneous amenorrhea for at least 12 consecutive months, spontaneous amenorrhea for at least 6 months with biochemical criteria or menopause (FSH > 40 IU/L), or bilateral oophorectomy for at least 6 weeks before the screening visit, or if premenopausal chemically suppressed by GnRH agonist therapy with ultrasensitive estradiol level <10.

On endocrine therapy for a minimum of 3 months and has planned duration of 12 weeks left in the treatment regimen. Participants receiving a CDK4/6 inhibitor must have been on treatment for at least 4 weeks prior to enrollment.

Experiencing an average of seven or more moderate to severe hot flashes per day over a 7-day period as documented by Symptom Diary during the Screening Period and seeking treatment or relief for VMS.

Able to swallow oral formulation of the study agent.

Exclusion Criteria:

Participants who have a diagnosis of stage IV metastatic disease.

Receiving any other cancer treatment other than endocrine therapy. This includes chemotherapy, targeted therapies, and immunotherapy.

Receiving cytochrome CYP1A2 inhibitors.

Participants who have initiated, discontinued, or had a dose adjustment of treatment for vasomotor symptoms (prescription, over the counter, or herbal) within 28 days prior to screening.

Pregnant or lactating patients.

Known cirrhosis or active liver disease, jaundice, or elevated liver aminotransferases (ALT or AST) >2x ULN, or elevated total bilirubin, OR elevated direct bilirubin, or elevated INR, or elevated alkaline phosphatase >2x ULN.

Creatinine > 1.5 times upper limit of normal; or estimated GFR ≤ 30 mL/min per 1.73 m2 at screening.

Judgement by the investigator that the participant should not participate in the study if the participant is unlikely to comply with study procedures, restrictions, and requirements.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Fezolinetant
Fezolinetant is an oral medication, and the first neurokinin 3 (NK3) receptor antagonist approved by the FDA in May 2023 for treatment of moderate to severe hot flashes due to menopause. It blocks the activities of the NK3 receptor which is involved in the brain's regulation of body temperature.
45 mg tablets, administered orally once daily with or without food, to be taken throughout the entire study phase, i.e. 12 weeks
Placebo Comparator: Placebo
Patients will be given placebo tablets to compare to active comparator.
45 mg tablets, administered orally once daily with or without food, to be taken throughout the entire study phase, i.e. 12 weeks

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Frequency of moderate/severe VMS at 12 weeks of treatment with fezolinetant vs. placebo
Time Frame: Baseline to 12 weeks
To evaluate the mean change reduction in frequency of moderate/severe VMS at 12 weeks of treatment with fezolinetant vs. placebo in breast cancer survivors on endocrine therapy (tamoxifen or aromatase inhibitors).
Baseline to 12 weeks

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Efficacy of fezolinetant vs. placebo in reducing the mean daily frequency of moderate/severe VMS
Time Frame: At week 4, after treatment initiation
To evaluate the efficacy of fezolinetant vs. placebo in reducing the mean daily frequency of moderate/severe VMS
At week 4, after treatment initiation
Regression of mean daily frequency of moderate/severe VMS average
Time Frame: Study duration: weeks 0-12
To evaluate treatment activity among breast cancer survivors treated with fezolinetant vs placebo over the entire course of the study duration - measure by regression of mean daily frequency of moderate/severe VMS average every week of treatment (weeks 0-12)
Study duration: weeks 0-12
Change in global quality of life using Functional Assessment of Cancer Therapy - Breast, Endocrine Therapy Symptoms (FACT-B ES)
Time Frame: Baseline to week 12
To evaluate the difference in global quality of life in breast cancer survivors treated with fezolinetant vs placebo using FACT-B ES. The total score range is 0 to 164, with higher scores indicating better quality of life
Baseline to week 12
Differences in sleep quality using PROMIS Sleep Disturbance-Short Form 8b (PROMIS SD SF 8b)
Time Frame: Baseline, week 4 and week 12
To evaluate the differences in sleep quality in breast cancer survivors' treatment with fezolinetant vs placebo using patient-reported outcomes measurement information System Sleep Disturbance - Short Form 8b (PROMIS SD SF 8b. Total score is calculated by summing the items (range: 8-40), with a higher score meaning more disturbed sleep.
Baseline, week 4 and week 12

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Collaborators

Investigators

  • Principal Investigator: Maryam Lustberg, MD, Yale University

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

December 5, 2025

Primary Completion (Estimated)

March 1, 2028

Study Completion (Estimated)

March 1, 2028

Study Registration Dates

First Submitted

April 1, 2025

First Submitted That Met QC Criteria

April 1, 2025

First Posted (Actual)

April 8, 2025

Study Record Updates

Last Update Posted (Actual)

June 2, 2026

Last Update Submitted That Met QC Criteria

May 30, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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