A Phase 3, Randomized, Double-blind Trial of Pembrolizumab (MK-3475) Plus Enzalutamide Plus ADT Versus Placebo Plus Enzalutamide Plus ADT in Participants With Metastatic Hormone-Sensitive Prostate Cancer (mHSPC) (KEYNOTE-991)
This research study, called KEYNOTE-991, is for men with prostate cancer that has spread to other parts of the body and is still sensitive to hormone treatment. The study wants to find out if adding a drug called pembrolizumab to the usual treatment (enzalutamide and hormone therapy) is more effective. Doctors will compare how well both groups respond by looking at how long it takes for the cancer to grow or spread further, and how long men live. This is a Phase 3 study, meaning it's one of the final steps before a new treatment might become widely available. Participants will be randomly assigned to receive either pembrolizumab or a look-alike inactive substance (placebo) along with their standard treatment, and neither they nor their doctors will know which they are receiving until the study ends.
At a glance
What is this study about?
This study is looking into a new treatment approach for men suffering from prostate cancer. Specifically, it focuses on a type of prostate cancer that has spread to other parts of the body (called metastatic) but still responds to treatments that lower male hormones (hormone-sensitive). The main goal is to see if adding a new drug, pembrolizumab, to the standard treatment can make a meaningful difference.
Currently, men with this type of prostate cancer often receive a combination of treatments, including hormone therapy and sometimes another drug like enzalutamide. This study wants to know if adding pembrolizumab to enzalutamide and hormone therapy works better than just enzalutamide and hormone therapy alone. 'Better' means whether it can stop the cancer from growing or spreading for longer, and potentially help men live longer.
Doctors will carefully observe how participants respond to the treatments. They will measure things like how long it takes for the cancer to show signs of growth or spread on scans (this is called 'radiographic progression-free survival') and overall survival, which means how long people live. They'll also look at other important factors like pain levels, changes in blood test markers (like PSA), and any side effects the treatments might cause. This helps them understand the full picture of how well a new treatment works and if it's safe.
Key takeaways
- This study is testing a new drug, pembrolizumab, for metastatic hormone-sensitive prostate cancer.
- It compares pembrolizumab plus standard treatment (enzalutamide and hormone therapy) with standard treatment alone.
- The main goals are to see if the new combination slows cancer growth and helps men live longer.
- Participants will be randomly assigned to a treatment group and carefully monitored.
- This is a Phase 3 study, a crucial step for new treatments.
Who may be eligible?
This study is designed for men who have prostate cancer that has spread to other parts of the body (metastatic) and is still responding to hormone therapy. Participants must be at least 18 years old.
There might be other specific health requirements or conditions that would mean someone cannot join the study. These are put in place to ensure patient safety and that the study results are as clear as possible.
It's important to discuss your full medical history with the study team to see if this trial is right for you.
- Are you a man?
- Are you at least 18 years old?
- Do you have prostate cancer that has spread to other parts of your body?
- Does your prostate cancer still respond to hormone treatment?
- Are you willing to have regular hospital visits, blood tests, and scans?
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 will be randomly placed into one of two groups. One group will receive pembrolizumab alongside enzalutamide and hormone therapy, while the other group will receive an inactive substance (placebo) instead of pembrolizumab, along with enzalutamide and hormone therapy. Neither you nor your doctor will know which group you are in.
You will have regular visits to the clinic for medical checks, blood tests, and scans to monitor your health and the cancer's progress. You will also be asked about any symptoms you're experiencing, including pain, and provide information about any other medications you are taking. The study will continue for a period, typically until your cancer shows signs of progression or if unacceptable side effects occur. Even after stopping the study medication, there will usually be follow-up appointments to continue monitoring your health.
Potential risks and benefits
Locations (3)
- —Denmark
- —Poland
- —Ireland
Common questions
What is 'metastatic hormone-sensitive prostate cancer'?
This means prostate cancer that has spread to other parts of your body, but tests show it still responds to treatments that lower male hormones.
What is pembrolizumab?
Pembrolizumab is a type of anti-cancer drug that helps your immune system fight cancer cells. It's often called immunotherapy.
What is enzalutamide?
Enzalutamide is a hormone therapy drug often used for prostate cancer. It blocks male hormones from telling cancer cells to grow.
What is a 'placebo'?
A placebo is an inactive substance that looks exactly like the study drug. It's used so neither you nor your doctor knows who is getting the active new drug, which helps make the study results accurate.
What does 'Phase 3' mean for this study?
Phase 3 is an advanced stage of drug development. It means the treatment has already shown some promise in earlier studies, and now researchers want to confirm its effectiveness and safety in a larger group of people before it can be considered for wider use.
How to find out more
Always speak to your GP or specialist before deciding to take part in a study.
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