A Study to Evaluate the Effect of GDC-4198 Alone and in Combination With Giredestrant Versus Abemaciclib and Giredestrant in Participants With Locally Advanced or Metastatic Estrogen Receptor-Positive (ER+), Human Epidermal Growth Factor Receptor-Negative (HER2-) Breast Cancer

To be considered for this study, you would need to have breast cancer that doctors have confirmed as locally advanced or metastatic, and it must be 'oestrogen receptor-positive (ER+)' and 'HER2-negative (HER2-)'. A key point is that your cancer must have continued to grow or spread even after you've had treatment with specific types of medicines for advanced cancer, including certain hormone therapies and a type of drug called CDK4/6 inhibitors.

You should also be generally well, able to perform your daily activities, and doctors expect you to live for at least six more months. They'll also check if your cancer can be measured or evaluated by scans.

There are also reasons why you might not be able to join. For example, if your cancer symptoms are very severe and doctors believe you need urgent chemotherapy, or if you've already had many different lines of treatment for your advanced breast cancer. Also, certain stomach or gut problems, other recent cancers (within the last three years, unless it was a very minor type), or allergies to the study drugs would prevent you from taking part.

If you decide to take part in this study, you'll be given either GDC-4198 by itself, or GDC-4198 with giredestrant, or abemaciclib with giredestrant. You'll have regular visits to the hospital for check-ups, which will include blood tests, physical examinations, and scans to see how the treatment is working. The study team will explain exactly what your schedule will involve, including how often you'll need to visit and for how long.

You'll be taking study medication, which will be provided to you. The doctors and nurses will monitor you closely for any side effects and to check your general health. After you finish taking the study treatment, there will be a follow-up period where the team will continue to check on your health and well-being. The total length of your participation will depend on how you respond to the treatment and the phase of the study you are in, but the team will give you a clear idea of the expected duration during the consent process.