RecruitingPHASE3INTERVENTIONAL

A Study of Tersolisib (LY4064809/STX-478) With Other Anti-Cancer Treatments in Participants With Advanced Breast Cancer With a Genetic Change (PIK3CA)

This research study is looking into a new drug called Tersolisib (also known as LY4064809 or STX-478). It's for people who have advanced breast cancer that's spread or can't be cured by surgery. To be eligible, your cancer must have a specific genetic change called PIK3CA. The study is combining Tersolisib with other established anti-cancer treatments to see if this new combination is safe and works better than current approaches. This is the first treatment for your advanced breast cancer in this study. The main goal is to find out if adding Tersolisib helps more than the usual treatments alone and how well people tolerate it.

At a glance

Status

Recruiting

Phase

PHASE3

Sponsor

Eli Lilly and Company

Enrolment target

920

Start

22 Dec 2025

Estimated completion

01 May 2033

Breast Neoplasms Neoplasm Metastasis

What is this study about?

This research study is for people who have advanced breast cancer, meaning it has either spread to other parts of the body (metastatic) or is locally advanced and can't be removed by surgery. The focus is on a specific type of breast cancer: one that is hormone receptor-positive (meaning its growth is fueled by hormones) and HER2-negative (meaning it doesn’t have high levels of the HER2 protein). A key requirement for this study is that your cancer must also have a particular genetic change called a PIK3CA mutation. This change can be found in your tumor or blood.

The study is investigating a new drug called Tersolisib. It's being given alongside other anti-cancer medications you might already be familiar with, such as Ribociclib, Palbociclib, Abemaciclib, Anastrozole, Letrozole, Exemestane, or Fulvestrant. These are common treatments for hormone receptor-positive breast cancer. The aim is to see if adding Tersolisib to these existing treatments makes them more effective at fighting the cancer and if this combination is safe for patients.

This is a 'Phase 3' study, which means it’s a big study that compares the new treatment combination to the standard treatment. Researchers want to see if the new approach is better than what's currently available. Patients will stay in the study for as long as the treatment is helping, and the side effects are manageable.

Key takeaways

This study is testing a new drug (Tersolisib) for advanced breast cancer.
It's for specific breast cancers with a PIK3CA genetic change, that are hormone receptor-positive and HER2-negative.
Tersolisib is given with other established anti-cancer medicines.
The aim is to see if this new combination is safe and more effective.
You must be 18 or older to participate.
This is likely to be your first treatment for advanced breast cancer.

Who may be eligible?

To join this study, you need to be at least 18 years old. Both men and women with breast cancer can participate. For women, whether you’ve already gone through menopause or not, you might be eligible, but if you're pre- or peri-menopausal, you'll need to use medication to suppress your ovarian function. Men with breast cancer will also need to use hormone suppression.

Your breast cancer must be advanced, meaning it has spread or cannot be treated with surgery. It also needs to be hormone receptor-positive and HER2-negative. Crucially, your cancer must have a specific genetic change called a PIK3CA mutation, which can be found in a sample of your tumor or blood. You should also have cancer that can be measured or evaluated.

For most people joining, this study would be your very first treatment planned for your advanced breast cancer. In some parts of the study, a small number of people who have had one or two previous treatments for advanced breast cancer, possibly including one chemotherapy, might be considered.

Quick self-check

Are you 18 years old or older?
Do you have advanced breast cancer that has spread or can't be operated on?
Has your doctor confirmed your breast cancer is hormone receptor-positive and HER2-negative?
Has your cancer been tested and confirmed to have a PIK3CA genetic change?
Is this your first treatment for advanced breast cancer? (Some exceptions may apply, ask your doctor.)
Are you able to use effective contraception if required?

This is a guide only — the research team will confirm whether you can take part.

What does participation involve?

If you decide to join this study, you might receive the new drug Tersolisib along with other standard anti-cancer medications, or you might receive the standard medications plus a placebo (a dummy pill). You won't know which group you are in. You'll have regular hospital visits, where doctors will check your general health, monitor your cancer with scans (like CT scans or X-rays), and take blood tests to see how you're responding to the treatment and to check for any side effects. You will need to use effective contraception if you are able to have children.

The specific schedule of visits and tests will be detailed by the study team, but they will happen regularly throughout the treatment period. You will continue to take the study medication for as long as it is helping control your cancer and you are tolerating the side effects. After stopping the study drug, there will be follow-up visits to monitor your health. The total duration of your involvement in the study will vary, depending on how long you benefit from the treatment.

Potential risks and benefits

Taking part in any clinical trial involves both potential benefits and risks. There's a chance the new treatment combination with Tersolisib could be more effective at treating your cancer than standard care alone, or it might help control the disease for longer. However, like all medications, Tersolisib and the other drugs can cause side effects. These could range from mild to severe, and the study team will monitor you closely for any issues. There's also no guarantee that the treatment will help your specific cancer. It's very important to remember that you have the right to withdraw from the study at any time, for any reason, without it affecting your future medical care.

Locations (327)

Alaska Oncology and Hematology
Anchorage, United States· Not yet recruiting
Ironwood Cancer & Research Centers
Chandler, United States· Not yet recruiting
Mayo Clinic in Arizona - Phoenix
Phoenix, United States· Not yet recruiting
The University of Arizona Cancer Center - North Campus
Tucson, United States· Not yet recruiting
Genesis Cancer and Blood Institute
Hot Springs, United States· Not yet recruiting
Highlands Oncology Group
Springdale, United States· Recruiting
Community Cancer Institute
Clovis, United States· Not yet recruiting
City of Hope
Duarte, United States· Not yet recruiting
Marin Cancer Care
Greenbrae, United States· Recruiting
Chao Family Comprehensive Cancer Center and Ambulatory Care (CIACC) - Irvine
Irvine, United States· Not yet recruiting
City of Hope Orange County Lennar Foundation Cancer Center
Irvine, United States· Not yet recruiting
Moores Cancer Center
La Jolla, United States· Not yet recruiting

+315 more sites — see the official record for the full list.

Common questions

What does 'advanced breast cancer' mean in this study?

It means the cancer has either spread to other parts of your body or is locally advanced and can't be treated with surgery.

What is PIK3CA?

It's a specific genetic change (mutation) found in some breast cancers. Your cancer must have this change to join the study.

Will I definitely get the new drug?

You might get the new drug Tersolisib plus standard treatment, or you might get standard treatment plus a placebo (a dummy pill). The treatment you receive will be chosen randomly.

How long will I be in the study?

You'll stay in the study as long as the treatment is helping your cancer and you're not having unbearable side effects. There'll also be follow-up appointments after you stop the treatment.

What if I decide I don't want to be in the study anymore?

You can leave the study at any time, for any reason, and it won't affect your future medical care.

How to find out more

Trial questions or participation questions: 1-877-CTLILLY (1-877-285-4559) or

LillyTrials@Lilly.com 1-317-615-4559 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.