Anti-HER2 treatment Discontinuation Guided by ctDNA in Patients with HER2-Positive Metastatic Breast Cancer with Sustained Disease Control: PHENIX Trial
The PHENIX trial is studying whether some people with secondary HER2-positive breast cancer can safely pause their treatment. Currently, targeted drugs such as Perjeta and Phesgo are given indefinitely to keep the cancer under control. However, these ongoing treatments can cause side effects and require frequent hospital visits. Doctors are using a special blood test called a ctDNA test, which looks for tiny traces of cancer DNA in the blood. If this test shows no signs of cancer, participants may be able to stop their medication and be monitored closely. If the blood test shows that cancer traces have returned, the treatment is restarted straight away. The trial aims to find out if taking a planned break from treatment is safe and whether it allows people to stay well over a two-year period.
At a glance
What is this study about?
HER2-positive breast cancer is a type of cancer where cells have high levels of a protein called HER2, which helps them grow. Modern treatments like Perjeta and Phesgo target this protein and are very effective. People living with secondary breast cancer (cancer that has spread) usually stay on these medicines for a very long time to keep the disease stable. However, having regular injections or drips can be tiring, time-consuming, and cause ongoing side effects.
This trial explores whether some patients can safely take a break from their anti-HER2 treatment. Doctors use a sensitive blood test called a 'liquid biopsy' to look for circulating tumour DNA (ctDNA). These are microscopic fragments of genetic material shed by cancer cells into the bloodstream. If these fragments cannot be detected, it suggests that the cancer is in deep remission.
In this study, patients whose blood tests show no detectable cancer DNA are given the opportunity to pause their treatment. They are then followed up very closely. If the blood tests show that cancer markers are rising again, doctors restart the treatment immediately to keep the cancer in check. The goal is to see if this approach gives people a safe break from medication without affecting their long-term health.
Key takeaways
- The trial tests whether patients with advanced HER2-positive breast cancer can safely pause treatment.
- A sensitive blood test (ctDNA) is used to check that no cancer traces are visible before pausing drugs.
- If cancer markers reappear in your blood, targeted treatment is restarted straight away.
- Participants will be closely monitored with regular tests and scans over two years.
- Joining is entirely your choice, and you can stop participating at any time.
Who may be eligible?
This trial is for adults aged 18 and over who have been diagnosed with HER2-positive breast cancer that has spread to other parts of the body. Both men and women can take part.
To be considered, your cancer must currently be well controlled by your targeted therapy, and you must have had stable disease for an extended time. A key requirement is that a special blood test shows no detectable traces of cancer DNA in your bloodstream.
Your hospital doctor or the study team will review your full medical history and recent scans to check if your general health and treatment history make this study suitable for you.
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.
- I am aged 18 or older.
- I have been diagnosed with HER2-positive secondary (metastatic) breast cancer.
- My cancer is currently stable and well controlled on anti-HER2 treatment (such as Perjeta or Phesgo).
- I am willing to have regular blood tests and clinic visits over a two-year period.
- I am comfortable with the idea of pausing treatment if tests show no signs of cancer DNA.
What does participation involve?
If you take part, you will first have blood tests to see if any cancer DNA is found in your bloodstream. If no traces are detected, you will be invited to pause your regular anti-HER2 treatment (such as Perjeta or Phesgo).
While off treatment, you will attend the clinic regularly for check-ups, blood tests, and routine hospital scans over a two-year follow-up period. These visits help doctors catch any early signs of the cancer becoming active again.
If tests show that cancer DNA has reappeared, your doctor will restart your targeted treatment right away. Overall, taking part involves frequent hospital visits for monitoring, regular blood draws, and staying in close contact with your care team for around two years.
Potential risks and benefits
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Common questions
What is a ctDNA test?
It is a simple blood test that checks for tiny pieces of DNA shed by tumour cells into your blood, helping doctors spot signs of cancer that scans might miss.
What happens if my cancer returns while I am on a break?
If the blood test or a scan shows any sign that the cancer is returning, your anti-HER2 treatment will be restarted promptly.
Do I have to stop my treatment if I join?
You will only be offered a break in treatment if your blood test shows no measurable signs of cancer DNA.
Can I leave the study if I change my mind?
Yes. You can leave the trial at any point and restart your standard medication, without it affecting your medical care.
Will taking part cost me anything?
No, the trial tests and study drugs are provided through the clinical trial. You may also be able to get help with travel costs to the hospital.
How to find out more
Always speak to your GP or specialist before deciding to take part in a study.
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