AuthorisedTherapeutic exploratory (Phase II)Interventional

UNLOCK - EPIBREAST, a phase II study of prifetrastat (PF-07248144), a KAT6 inhibitor, plus fulvestrant for advanced HR+/HER2- breast cancer with biomarkers analysis

This research, called UNLOCK - EPIBREAST, is a Phase II study looking into a new drug called prifetrastat. It's combined with a drug already used, fulvestrant, for advanced breast cancer. This is for breast cancer that is hormone receptor-positive (HR+) and HER2-negative, and has continued to grow despite earlier treatments, specifically those including common hormone therapies and CDK4/6 inhibitors. The main goal is to see how well this new combination shrinks tumors and slows cancer growth. Researchers will also look at how the drugs affect cancer cells to better understand how they work and identify patients who might benefit most. This is an important step in finding new ways to treat breast cancer.

At a glance

Status

Authorised

Phase

Therapeutic exploratory (Phase II)

Sponsor

Unicancer

Enrolment target

Start

22 May 2026

Adult patients with advanced hormone receptor positive (HR+), HER2- breast cancer after at least a first line of endocrine therapy combined with CDK4/6 inhibitor in the metastatic setting

What is this study about?

This study, called UNLOCK - EPIBREAST, is looking for new ways to treat advanced breast cancer. Specifically, it's for a type of breast cancer that relies on hormones to grow (we call this hormone receptor-positive, or HR+) and doesn't have too much of a protein called HER2 (so, HER2-negative). This study is for people whose cancer has unfortunately come back or grown after receiving at least one previous treatment combination, which would have included hormone therapy and a type of drug called CDK4/6 inhibitors.

The main aim of this study is to test a new drug, prifetrastat, alongside an existing treatment, fulvestrant. Fulvestrant is already used to treat HR+ breast cancer. Researchers want to see if adding prifetrastat makes the treatment more effective at stopping the cancer from growing or even making it shrink. They'll be carefully monitoring how the cancer responds to this new combination.

Beyond just seeing if the treatment works, the study also wants to understand *how* prifetrastat affects cancer cells. They will be looking at tiny changes in the cancer cells and their genes to figure out why the treatment might work for some people and not others. This information is vital for developing better, more targeted treatments for breast cancer in the future.

Key takeaways

Tests a new drug (prifetrastat) with an existing one (fulvestrant).
For advanced, hormone receptor-positive, HER2-negative breast cancer.
For patients whose cancer grew after previous hormone/CDK4/6 inhibitor treatment.
Aims to see how well the treatment works and how it affects cancer cells.
It's a Phase II study, continuing to check effectiveness and safety.

Who may be eligible?

This study is for adults, 18 years and older, who have a specific type of advanced breast cancer. Your breast cancer needs to be hormone receptor-positive (HR+) and HER2-negative. This means your cancer cells have receptors that respond to hormones and they don't have high levels of the HER2 protein.

You would also need to have received previous treatments for your advanced breast cancer. Specifically, your cancer must have grown or spread after being treated with at least one line of hormone therapy combined with a CDK4/6 inhibitor (a common type of drug used for this kind of cancer) while it was advanced or metastatic (meaning it had spread to other parts of the body).

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you 18 years old or older?
Do you have advanced breast cancer that is hormone receptor-positive (HR+)?
Is your breast cancer HER2-negative?
Has your advanced breast cancer grown or returned after treatment with a hormone therapy and a CDK4/6 inhibitor?

Answer every question to see your result.

What does participation involve?

If you join this study, you will receive the new drug, PF-07248144 (prifetrastat), along with fulvestrant. Fulvestrant is given as an injection. Researchers will take blood samples at different times to check how the treatment affects your cancer and to look for changes in your DNA circulating in the blood. They will also collect tissue samples if possible. You will have regular scans (like CT scans or bone scans) to measure how your cancer is responding. The study duration will depend on how you respond to the treatment, with regular follow-up visits and assessments over several months or longer.

Potential risks and benefits

Taking part in a clinical trial might offer potential benefits, such as access to a new treatment that isn't yet widely available, which could be more effective than standard options. However, there are also potential risks, including side effects from the study drugs that are not yet fully known. Your doctors will carefully monitor you for any side effects. You are free to withdraw from the study at any time, for any reason, without it affecting your future medical care.

Locations (1)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

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Unverified
France

Common questions

What is 'advanced HR+/HER2- breast cancer'?

This means breast cancer that has spread beyond the breast (advanced) and whose cells are 'hormone receptor-positive' (they grow in response to hormones) but 'HER2-negative' (they don't have too much of a protein called HER2).

What is a 'Phase II study'?

A Phase II study is an early stage of clinical research where a new treatment is given to a larger group of people to see if it's effective and safe, after initial small-scale testing.

What are 'biomarkers'?

Biomarkers are biological signs in your body, like certain changes in your genes or proteins, that can help doctors understand your cancer better and predict how it might respond to treatment.

What are 'endocrine therapy' and 'CDK4/6 inhibitor'?

These are common types of treatments for HR+ breast cancer. Endocrine therapy aims to block hormones, and CDK4/6 inhibitors are drugs that slow down cancer cell growth.

Will I know if the new drug is working?

Yes, the study involves regular checks, including scans and blood tests, to see how your cancer is responding to the treatment. Your study doctor will discuss these results with you.