A study of G1T38 for breast cancer that has spread

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

Cancer type:

Breast cancer
Secondary cancers




Phase 1/2

This study is looking at a drug called G1T38 with fulvestrant for breast cancer that has spread (advanced breast cancer).

It is open to people with advanced breast cancer that has continued to get worse while having hormone therapy

More about this trial

Fulvestrant is a type of hormone therapy doctors use for advanced breast cancer. They can use it after other hormone therapies have stopped working. 
G1T38 is a targeted cancer drug. It works by stopping an enzyme Open a glossary item that cancer cells need to grow and multiply. 
We know from laboratory studies Open a glossary item that G1T38 can stop the growth of cancer and might even make it smaller. 
In this study researchers want to know if G1T38 can help people who are having fulvestrant when other hormone therapy stopped working. 
Before this they need to find the best dose of G1T38 to give with fulvestrant. 
The aims of this study are to find:
  • the best dose of G1T38 to have with fulvestrant
  • how well G1T38 with fulvestrant works for advanced breast cancer
  • what the side effects are

Who can enter

The following bullet points list the entry conditions for this study. 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
This trial is open to men and women. 
You may be able to join this study if all of the following apply. You:
  • have breast cancer that has spread to the surrounding tissue (local spread) or to another part of the body (metastatic) that can’t be treated with the aim to cure
  • have breast cancer that has receptors for hormones (oestrogen receptor positive Open a glossary item and, or progesterone Open a glossary item receptor positive breast cancer) 
  • are a woman who has gone through the menopause Open a glossary item, if you haven’t gone through the menopause you might be able to join the trial if you are able to take the LH blocker Open a glossary item drug goserelin 
  • have had treatment and your breast cancer continued to get worse during treatment or within 2 months and up to a year after treatment depending on what treatment you had
  • have an area of cancer that can be measured
  • can do anything apart from heavy physical work (performance status 0 or 1)
  • have satisfactory blood test results
  • are willing to use reliable contraception during treatment and for 4 months after if you or your partner could become pregnant
  • can swallow capsules whole
  • are at least 18 years old
Who can’t take part
You cannot join this study if any of these apply. 
Cancer related
  • have cancer that has spread to the brain or spinal cord unless it has been treated, you have no symptoms and haven’t had medication to control fits and steroids for a month before starting G1T38
  • have cancer that has a high number of the HER2 Open a glossary item protein (HER2 positive)
  • have had previous treatment with a similar drug to G1T38 (a CDK inhibitor) or fulvestrant 
  • are taking another experimental drug within 4 weeks of starting G1T38  
  • have had chemotherapy within 3 weeks before starting G1T38 
  • are to have radiotherapy 
  • have radiotherapy within 2 weeks of starting G1T38
  • have had radiotherapy to the area of cancer that is to be measured as part of the trial
  • have had radiotherapy to more than a quarter (25%) of your bone marrow Open a glossary item
  • are not on a stable dose of bisphosphonates Open a glossary item or denosumab within 2 weeks of starting G1T38
  • have had a stem cell transplant Open a glossary item or bone marrow transplant Open a glossary item
  • have another cancer apart from successfully treated non melanoma skin cancer Open a glossary item, in situ cancer Open a glossary item of the cervix, prostate cancer, early bladder cancer or any other cancer that was treated with the aim to cure and there hasn’t been any sign of it for at least 3 years
  • still have ongoing moderate to severe side effects from previous treatment apart from hair loss and nerve damage (peripheral neuropathy)
Medical conditions
You can’t take part if you:
  • are taking medication that affects the CYP enzymes within 2 weeks of starting G1T38
  • have major surgery within 2 weeks of agreeing to take part in the study
  • are taking steroids unless it is to a small dose (10mg or less) to replace steroids in the body, is used to stop feeling sick, is a spray or a short course (up to 10 days) of tablets or cream for allergies or asthma
  • have had a stroke, heart attack within the past 6 months or another serious heart condition such as congestive heart failure
  • have HIV, hepatitis B, hepatitis C or another serious active infection
  • have a problem with your digestive system Open a glossary item
  • have a problem with bleeding or are taking medication, such as warfarin, to stop your blood clotting
  • have another medical or mental health condition that your doctor or the study team think could affect you taking part
You can’t take part if you:
  • are allergic or sensitive to fulvestrant or any of its ingredients
  • are allergic or sensitive to LH blockers or any of their ingredients
  • are pregnant or breastfeeding

Trial design

This is a phase 1/2 study. It is in 2 parts. The team need 72 people to join the 1st part. And up to 30 people to join the 2nd part. 
Part 1
In this part the first few people will have a low dose of G1T38 with fulvestrant. If they don’t have any bad side effects the next few will have a higher dose of G1T38 with fulvestrant. And so on until researchers find the best dose of G1T38 to give with fulvestrant. 
Part 2
In this part everyone has the best dose of G1T38 from part 1 with fulvestrant. 
G1T38 is a tablet. You take it with food either once a day or twice a day. Your doctor will tell how many and how often to take the tablets. 
Fulvestrant is an injection you have into a muscle. You have 2 injections:
  • every 2 weeks for 3 doses
  • then every 4 weeks
You continue having treatment as long as it is helping and the side effects aren’t too bad. 
The study team will ask for a small piece of the cancer tissue that was taken when you were first diagnosed. 
They will also ask if you are willing to have more samples of tissue taken during the study. You don’t have to agree to this. You can still take part in the study.
Researchers will use these samples to look for substances (biomarker Open a glossary item) that might tell them how well the treatment works. 
The team will take extra blood samples and urine samples. They will use these to find out what happens to G1T38 in the body and how well it is working.

Hospital visits

You see the doctor for tests before taking part in the study. These tests include:
During treatment you see the doctor every week for 9 weeks and then every 2nd week.
You have a CT scan or MRI scan every 2 months. 
You see the doctor after you finish treatment for:
  • a physical examination
  • blood tests
  • heart trace
After treatment you see the doctor every 3 months, or a member of the study team will phone you.

Side effects

Your doctor and nurse will monitor you closely for any side effects. Let your doctor or nurse know as soon as possible if:
  • you have severe side effects 
  • your side effects aren’t getting any better
  • your side effects are getting worse
G1T38 is a new drug and there may be side effects we don’t know about yet. Based on other studies using G1T38 and similar drugs the common side effects can include:
We have information about the side effects of fulvestrant
Your doctor or a member of the study team will talk to you about the possible side effects of G1T38 and fulvestrant before you agree to take part. 

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 Rebecca Roylance

Supported by

G1 Therapeutics
University College London Hospitals NHS Foundation Trust

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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