A study looking at ribociclib and letrozole for people with advanced breast cancer (COMPLEEMENT-1)

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

Cancer type:

Breast cancer




Phase 3

This study is for people with breast cancer that has come back in the area where it was first found, or that has spread elsewhere in the body.

It is open to men and women whose breast cancer cells have:

  • receptors for oestrogen or progesterone (hormone receptor positive)
  • low or no amounts of HER2 (HER2 negative breast cancer)

Also, they have not had any hormone therapy for their advanced breast cancer.

More about this trial

Some breast cancers have hormone receptors. A receptor allows a hormone to bind to a cell. Oestrogen and progesterone are sex hormones that are made naturally in the body. But they can stimulate some breast cancers to grow by triggering particular proteins (receptors) in the cancer cells.

Cancers that have these hormone receptors are called hormone receptor positive. If you have a hormone receptor positive cancer you usually have treatment with a hormone therapy.

Hormone therapies slow the growth of your cancer by stopping hormones from reaching cancer cells.

If your breast cancer cells have a lot of a protein called human epidermal growth factor (HER2) then a drug called trastuzumab (Herceptin) can be used. It attaches to the HER2 protein and stops the cells growing and dividing. But Herceptin won't work if you are HER2 negative. So doctors want to find other treatments for people in this situation.

In this study everyone has

Letrozole is a standard treatment for people with hormone receptor positive breast cancer.

Ribociclib blocks certain proteins, called cycline dependent kinase. Cells need these proteins to divide. They might also control the ability of breast cancer to grow.

Men and pre menopausal women in this study also have a drug called goserelin or leuprorelin. These drugs are a type of hormone therapy. It stops the production of the hormone oestrogen and so lowers the amount of oestrogen in the body.

Doctors want to learn more about how safe it is to have ribociclib alongside letrozole and whether this is a useful treatment for advanced breast cancer.

Who can enter

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

You may be able to join this study if all of the following apply.

  • You have breast cancer that has come back in the area where it was first found (locoregionally recurrent) or it has spread elsewhere in the body (metastatic or secondary breast cancer)
  • You are not able to have any treatment to cure your cancer
  • Your breast cancer is hormone receptor positive and HER2 negative
  • 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 have satisfactory results from an ECG Open a glossary item
  • You are able to swallow tablets
  • You are willing to use reliable contraception during the study and for 3 weeks after stopping the trial treatment if you or your partner could become pregnant
  • You are aged 18 or older

You cannot join this study if any of these apply.

Cancer related

  • You have had hormone therapy for your advanced breast cancer. You may still be able to take part if you have taken either letrozole or anastrozole for less than 28 days. If you have had hormone therapy with either letrozole or anastrozole for early breast cancer Open a glossary item then you must have completed this at least 12 months ago
  • You have had previous treatment with drugs that work in the same way as ribociclib (CDK4/6 inhibitors)
  • You are currently having any type of anti cancer treatment. Any chemotherapy or anti cancer treatment must have finished at least 7 days ago, or you must have no traces of the treatment in your bloodstream. You must not have had more than 1 course of chemotherapy
  • You have had radiotherapy in the last 4 weeks (in the last 2 weeks if it was radiotherapy for symptoms given only to a small area of your body)
  • You have had an experimental treatment as part of a clinical trial in the last month
  • You haven’t recovered from side effects of previous anti cancer treatments (apart from hair loss) unless they are mild
  • You have had surgery in the last 2 weeks and haven’t recovered from the side effects
  • You have cancer that has spread to the brain or spinal cord unless you have had treatment that finished at least 28 days ago, it is stable and you haven’t taken steroids or drugs to control seizures in the last 2 weeks
  • You have had any other cancer in the last 3 years apart from early cancer of the cervix or non melanoma skin cancer that was successfully treated

Medical conditions

  • You have a problem with your digestive system that might affect how you absorb the drug
  • You have problems with your heart, such as a heart attack in the last year, high blood pressure that is not well controlled, angina that is not well controlled, an abnormal rhythm of your heart, congestive heart failure that is causing symptoms, a very slow heart rate or the left side of the heart isn’t working well
  • You have high blood pressure that is not controlled
  • You are taking certain medications that affect body substances called CYP enzymes, this includes some herbal remedies and dietary supplements. You may be able to take part if you can stop taking these within 7 days of starting treatment in this study 
  • You have had steroids in the last 7 days unless you have had these as inhalers, creams, eyedrops or as local injections
  • You are known to have HIV
  • You have any other serious medical condition that the study team think could you taking part such as long term problems with your pancreas (chronic pancreatitis), active hepatitis, and an active untreated or uncontrolled infection
  • You are pregnant or breast feeding


  • You are allergic or sensitive to ribociclib or letrozole or anything they contain

Trial design

This is a phase 3 international trial. Researchers need around 3000 people from several different countries to join the study. They hope at least 100 people in the UK will take part.

Ribociclib and letrozole are both tablets. You take:

  • 3 tablets of ribociclib once a day for 21 days
  • 1 tablet of letrozole once a day for 28 days

Men and pre menopausal women have goserelin or leuprorelin as an injection. You have this as an injection just under the skin (a subcutaneous injection), usually into your tummy. You go to hospital once a month to have this. A nurse will give you the injection.

Each 28 day period is a cycle of treatment. When 1 cycle finishes, you start the next cycle. You have treatment for up to 2 years, as long as it is helping you and the side effects aren’t too bad.

You must avoid eating the following for 7 days before starting and during all of your treatment:

  • grapefruit
  • pomelo (or pummelo)
  • star fruit
  • Seville oranges (including marmalades made with these)

You must also avoid drinking the juice of any of the above.

Quality of life
Women are asked to complete some questionnaires:

  • every 4 weeks for the first 6 months
  • every 8 weeks for a further 6 months
  • then every 3 months until you finish treatment

The questionnaires ask about any side effects you’ve had and how you have been feeling. This is called a quality of life study.

Hospital visits

You see the doctors and have some tests before you start treatment. The tests include:

During the time you take the study drugs you need to go to the hospital for a check up:

  • twice in the first 2 months
  • once a month for the next 3 months
  • every 8 weeks for the next 6 months
  • then every 3 months

For the first 6 months you have regular blood tests and ECGs during your check ups. You then only have these if your doctor thinks it is necessary.

If you are having goserelin or leuprorelin, you go to hospital once a month for your injections.

You have a CT or MRI scan every 3 months.

When you stop treatment you see the study team within 1 week and again one month later. You have most of the same tests you had before starting the study.

Side effects

The study team will monitor you during the time you have treatment and you are given a phone number to call if you are worried about anything.

The most common side effects of ribociclib include:

Your nurse will explain all the possible side effects to you in more details. You have a contact number to ring in case you have any questions or concerns.

We have information about:

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

Dr Alistair Ring

Supported by


If you have questions about the trial please contact our cancer information nurses

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.

Last reviewed:

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