A trial looking at whether ctDNA can help doctors know who is at risk of breast cancer coming back and if pembrolizumab reduces ctDNA (c-TRAK TN)

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

Cancer type:

Breast cancer




Phase 2

This trial is looking at finding circulating tumour DNA (ctDNA) from breast cancer. Doctors may then treat them with pembrolizumab. 

It is for people who have completed their main treatment for triple negative breast cancer (TNBC). Triple negative breast cancers are cancers whose cells don’t have receptors for:

  • the hormones oestrogen and progesterone
  • the HER2 protein

More about this trial

Surgery, chemotherapy and radiotherapy are the main treatments for triple negative breast cancer. You usually don’t have more treatment after your main treatment has finished. Your doctor will monitor you regularly to look for signs of the cancer coming back. This is your follow up.

Researchers know that when breast cancer cells die, they can release small pieces of DNA into the bloodstream. This is called circulating tumour DNA (ctDNA). So doctors have developed a new test that looks for ctDNA in the blood.

Doctors think that the new test can help to tell who is at risk of the cancer coming back (relapse).

This trial is in 2 parts. In the 1st part, everyone has blood tests to look for ctDNA.

The 2nd part of this trial is for people who have ctDNA found in their blood.  They will have either:

  • pembrolizumab
  • regular blood tests only (observation group)

Pembrolizumab (Keytruda) is a type of immunotherapy. It stimulates the body’s immune system to fight cancer cells.

The main aims of this trial are to:

  • find out if the blood test can give an early indication as to who is at risk of the cancer coming back
  • see if pembrolizumab can get rid of ctDNA and stop breast cancer from coming back

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.

Who can take part
You may be able to join this trial if all of the following apply:

  • you have early stage triple negative breast cancer (TNBC)
  • your doctor thinks that there is a high or moderate risk of your cancer coming back
  • you have samples of tissue taken during a biopsy to diagnose your cancer or during breast cancer surgery that can be given to the study team
  • you have had surgery in the last 6 weeks, or you have recently started standard adjuvant chemotherapy, or you have going to start adjuvant chemotherapy with capecitabine
  • you are well enough to be up and about for at least half the day (performance status 0, 1 or 2)
  • you have satisfactory blood tests
  • you are willing and able to have blood samples taken for research
  • you are willing to receive pembrolizumab treatment, if you are randomised to do so
  • you are at least 16 years old
  • you are willing to use reliable contraception during treatment and for 4 months after the last dose of pembrolizumab (if you have this), if there is any possibility you or your partner could become pregnant

Who can’t take part
You cannot join this trial if any of these apply.

Cancer related

  • have breast cancer that has spread to other parts of the body (metastatic)  
  • are having, or are going to have, treatment for breast cancer apart from surgery, or radiotherapy and chemotherapy given in addition to surgery (adjuvant treatment)
  • have had treatment with a targeted cancer drug (biological therapy) in the last 4 weeks
  • have had pembrolizumab before or any other similar drug
  • have had another cancer in the last 5 years apart from basal cell skin cancer or carcinoma in situ of the cervix that have been successfully treated 

Medical conditions

  • are taking part in another clinical trial, or have taken part in a clinical trial that continued after your breast cancer surgery  
  • have had an experimental treatment in the past month
  • have or have had an autoimmune disease that needed treatment that reached your whole body (systemic treatment) in the past 2 years, apart from treatment to replace something the body makes such as insulin or thyroxine
  • have taken drugs that damp down your immune system (immunosuppressants) such as steroids in the week prior to the start of treatment
  • have moderate or severe side effects from previous treatment, apart from hair loss (alopecia) or problems with your nerves (neuropathy), that have not recovered before the start of treatment 
  • have lung problems such as inflammation of the lungs (pneumonitis)
  • have tuberculosis
  • have HIV
  • have hepatitis B or hepatitis C
  • have an active infection
  • have had an organ transplant or allogenic stem cell transplant in the past 
  • have any other medical condition that the trial team thinks could affect you taking part


  • are pregnant or breastfeeding
  • have had a live vaccine in the past month (prior to the start of treatment)

Trial design

This is a phase 2 trial. The researchers need around 200 people to join the 1st part of the trial and they think that up to 68 of those people will join the 2nd part.

First, the trial team asks to use tissue samples (archival tumour samples) that were taken during a biopsy or during surgery. You also have a blood test. Doctors want to look for a change (a mutation) in your genes.

Only people who have certain changes in their genes will be able to join the 1st part of this trial. Your doctor can tell you more about this.

Part 1
Everyone taking part has blood tests to look for circulating tumour DNA (ctDNA). This part is called ctDNA screening.

You have blood tests every 3 months, for up to 2 years.

If you have ctDNA found in your blood within the first year of ctDNA screening, you will be randomised into part 2 of the study.

If you do not have ctDNA found within the first year:

  • you have another year of ctDNA screening blood tests
  • then you are followed up every 6 months

Part 2
Only people who have ctDNA found in their blood during the 1st year of ctDNA screening (part 1) go into the 2nd part of this trial.

This part of the trial is randomised. The people taking part are put into 1 of the following treatment groups by computer:

  • pembrolizumab
  • regular blood tests only (observation group)

You are 2 times more likely to go into the pembrolizumab group than the observation group. Neither you nor your doctor are able to decide which group you are in. You and your doctor will only be told if you are randomised to have pembrolizumab.

If you are randomised to have pembrolizumab, doctors will check that you meet all the entry criteria. You have pembrolizumab as a drip into a vein every 3 weeks. You can have treatment for up to a year.

If you are randomised into the observation group, neither you or your doctor will know. You continue to have blood tests every 3 months for up to 2 years. Doctors want to continue to look for ctDNA in your blood.

c-TRAK TN Diagram

Blood tests
Some hospitals will ask for extra blood samples. Researchers want to look for changes in your immune system that can help to tell why treatments work better for some people than others.  Your doctor can tell you more about this.  

Hospital visits

You see the doctor and have some blood tests before taking part.

During the 1st part of the trial, you have a blood test every 3 months. This continues for up to 2 years.

If ctDNA is found in your blood within the first year and you are randomised to have pembrolizumab, you will see the doctor again and have some tests before having treatment in the 2nd part of this trial. The tests might include:

  • blood tests
  • physical examination
  • heart trace (ECG)
  • a CT scan, bone scan or PET-CT scan
  • urine sample

If you are well enough to have treatment, you will see the doctor and have pembrolizumab treatment every 3 weeks. You also have blood tests before each pembrolizumab treatment. This continues for up to a year.

When you stop pembrolizumab, you see the trial team and continue to have blood tests every 3 months for another year.

If you are randomised to the observation group, you continue to have blood tests that look for ctDNA. You have blood tests for up to 2 years from when you entered the trial.

After you finished the ctDNA screening, you see or speak with the trial team every 6 months. This is to check how you are.

Side effects

The trial team monitor you during the time you have the blood tests and treatment (if you are randomised to have pembrolizumab). You have 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 the side effects of 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 Nicholas Turner

Supported by

Cancer Research UK
Merck, Sharp & Dohme
NIHR Royal Marsden Biomedical Research Centre
The Institute of Cancer Research (ICR)
The Royal Marsden NHS Foundation Trust

Other information

This is Cancer Research UK trial number CRUKE/16/024

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.

Harriet wanted to try new treatments

Picture of Harriet

“I was keen to go on a clinical trial. I wanted to try new cancer treatments and hopefully help future generations.”

Last reviewed:

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