A trial looking at pembrolizumab for men with prostate cancer (KEYNOTE-199)

Please note - this trial is no longer recruiting patients. We hope to add results when they are available.

Cancer type:

Prostate cancer




Phase 2

This trial is for men with prostate cancer that has continued to grow or spread (metastatic cancer) despite hormone treatment.

It is for men who either: 

  • have had chemotherapy with a drug called docetaxel - this group is now closed
  • have had hormone treatment with a drug called enzalutamide. And haven't had chemotherapy with docetaxel

More about this trial

Prostate cancer can be treated with hormone therapy. But after some time, it may start to grow again. Doctors call this castration resistant prostate cancer.

If this happens, doctors can give chemotherapy. Often a drug called docetaxel is used.

But doctors are looking at new ways to help men in this situation. In this trial, they are looking at a drug called pembrolizumab (also called Keytruda).

Pembrolizumab is already used to treat other types of cancer. It is a type of biological therapy called a monoclonal antibody.

Researchers think it may help your immune system attack the cancer and stop it from growing.

The aims of this trial are to:

  • find how well pembrolizumab works as a treatment
  • learn more about side effects
  • find out what happens to pembrolizumab in your body (pharmacokinetics Open a glossary item)
  • learn how well people cope with side effects  

Who can enter

The following bullet points list the entry conditions for this trial. Talk to your doctor or the trial team if you are unsure about any of these. They will be able to advise you.

You may be able to join this trial if you are a man and all of the following apply

  • You have adenocarcinoma of the prostate (prostate cancer)
  • Your cancer has grown into surrounding tissue and cannot be removed with surgery, or has spread to another part of your body (metastatic cancer) 
  • You have an area of prostate cancer that can be seen and measured on a scan or areas of cancer in your bones (bone metastases Open a glossary item) that can be seen on a scan  
  • You are not able to have any treatment to cure your cancer
  • Your PSA and scans show that your cancer is getting worse in the past 6 months 
  • You have had a sample of cancer taken (a biopsy Open a glossary item) or are willing to have 1 taken – the doctor will check for this 
  • You have had at least 1 type of hormone treatment to reduce the level of testosterone Open a glossary item (such as abiraterone or enzalutamide)
  • You have had treatment with a chemotherapy drug called docetaxel or a hormone therapy called enzalutamide
  • You have very low levels of the male hormone testosterone (less than 50 ng/dL). If you haven’t had surgery to remove the testicles (orchidectomy) and are taking drugs to stop the testicles making testosterone you must have started them at least 4 weeks ago
  • You are well enough to be up and about for at least half of the day (performance status of 0, 1 or 2)
  • You have satisfactory blood tests results
  • You are at least 18 years old
  • You are willing to use reliable contraception during treatment and for 120 days (about 4 months) after the final dose of pembrolizumab if there is any possibility your partner could become pregnant

You cannot join this trial if any of these apply:

  • You have a rare type of prostate cancer called small cell prostate cancer  
  • Your cancer has spread to your brain or the tissues surrounding your brain (carcinomatous meningitis). If your cancer has spread to your brain and you have had treatment for this, you may be able to take part if it is stable, you have no symptoms and you have not had steroids in the past 7 days  
  • You have had another cancer in the last 3 years apart from basal cell skin cancer Open a glossary item, squamous cell skin cancer or carcinoma in situ (CIS) of the cervix that has been successfully treated
  • You have had radiotherapy, hormone therapy or chemotherapy in the past 2 weeks (4 weeks if it was a monoclonal antibody)
  • You have had more than 2 different types of chemotherapy or more than 3 if it was a combination of chemotherapy and hormone therapy     
  • You have had the drug pembrolizumab or any other drug that affects a protein called PD-1 or certain immune cells called T-cells 
  • You have had an experimental drug or used an experimental device as part of a clinical trial in the past 4 weeks
  • You have moderate to severe side effects from previous anti cancer treatments (apart from hair loss and numbness and tingling in your hands and feet)
  • You take drugs to stop or slow down bone damage (such as bisphosphonates Open a glossary item) and have not been on a stable dose in the past 4 weeks   
  • You have inflammation of the lungs (pneumonitis) that needs treatment with steroids or a lung condition called interstitial lung disease
  • You have a problem with your immune system Open a glossary item and have taken drugs to damp it down (immunosuppressants) such as steroids in the past 7 days (unless it was a small dose to help with your symptoms) 
  • You have an autoimmune disease that needed treatment that reached your whole body (systemic treatment Open a glossary item) in the past 2 years, unless it was treatment to replace something the body makes such as thyroxin and insulin Open a glossary item     
  • You have an active infection Open a glossary item
  • You have HIV
  • You have hepatitis B or hepatitis C
  • You have had a live vaccination Open a glossary item in the past 30 days
  • You have any other serious medical condition or mental health problem that the trial team think could affect you taking part

Trial design

This is an international phase 2 trial. The researchers need about 370 people to take part worldwide.

This trial is for men who either:

  • have had chemotherapy with docetaxel (cohort 1, 2 and 3) - these groups are now closed
  • have had hormone treatment with enzalutamide and haven't had chemotherapy with docetaxel (cohort 4 and 5) - only cohort 4 is open

Doctors are currently looking for men who have had enzalutamide. And their cancer started to grow again after some time (cohort 4). 

Everyone taking part has pembrolizumab. You have it as a drip into a vein every 3 weeks. It takes about 30 minutes.

You continue to have pembrolizumab for as long as your cancer does not get worse and the side effects aren’t too bad. You can have it up to 35 times (over about 2 years).

If your cancer goes away and then comes back again, you may be able to have an extra 17 treatments. This is called second course treatment. Your doctor can tell you more about this.  

Men who take part in cohort 4 and 5 also have enzalutamide. Your doctor can tell you more about this, and what to expect.  

Blood tests
You have some extra blood tests as part of this trial. The researchers want to find out what happens to pembrolizumab in the body (pharmacokinetics).

They also want to look for substances called biomarkers Open a glossary item to see why treatments work better for some people than others.

Researchers store your blood samples for up to 15 years. They may ask you if they can use these samples in future studies. This is called future biomedical research.

You don’t have to agree to have your blood used in future studies if you don’t want to. You can still take part in this trial.

Tissue samples
You also need to give a tissue sample (biopsy) of your cancer before you start treatment. This is to check if there is a marker on your cancer called PD-L1.

Researchers ask to use a tissue sample of your cancer taken either when you were diagnosed or during other treatments. You may also need to have a biopsy. The doctors can tell you more about this.    

They might also ask to store your tissue samples and use them in future studies (future biomedical research). Again, you don’t need to agree to this research if you don’t want to. You can still take part in the trial.   

Quality of life
Everybody taking part completes a quality of life questionnaire:

  • before starting treatment
  • at set times during the trial
  • after you finish treatment

The questionnaire asks about side effects and how you have been feeling.

Hospital visits

You see a doctor and have some tests before taking part. These tests include:

You see the doctor for blood tests and a physical examination every 3 weeks.

You have a CT or an MRI scan every 9 weeks while you are having treatment. After 12 months you have a CT or an MRI scan every 12 weeks.

This continues for as long as your cancer stays the same and does not get worse. If your cancer gets worse you stop having pembrolizumab.

When you finish your treatment, you see the trial team:

  • after 4 weeks
  • then every 9 weeks

After 12 months the trial team will phone you every 12 weeks to see how you are.

Side effects

The trial team monitor you during the time you have treatment. You are given a phone number to call them if you are worried about anything.  The team will tell you about all the possible side effects before you start the trial.

The most common side effects of pembrolizumab are:

We have more information about pembrolizumab.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Johann De Bono

Supported by

Merck, Sharp & Dohme

Freephone 0808 800 4040

Last review date

CRUK internal database number:


Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Keith took part in a trial looking into hormone therapy

A picture of Keith

"Health wise I am feeling great. I am a big supporter of trials - it allows new treatments and drugs to be brought in.”

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