Study Comparing RO7771950 and Tucatinib with Trastuzumab and Capecitabine for Advanced HER2-Positive Breast Cancer

Inclusion Criteria

• Have advanced breast cancer that cannot be surgically removed or has spread to other parts of the body, confirmed to be HER2-positive.
• Have measurable cancer as defined by specific medical criteria in the first stage of the study. Non-measurable cancer is allowed in the second stage.
• Have had brain metastases that are stable, progressing, or previously untreated, or cancer that has spread to the membranes around the brain and spinal cord.
• Have received at least one previous treatment targeting HER2 for advanced or metastatic cancer.
• Have previously received certain anti-HER2 treatments, like trastuzumab-deruxtecan or trastuzumab emtansine, unless these treatments are not available or suitable for you.
• Have taken a specific type of cancer drug called a tyrosine kinase inhibitor more than 12 months before the cancer became advanced, but not for advanced or metastatic cancer.
• Have adequate organ and bone marrow function as defined by the study.
• Have a performance status score of 0 or 1, indicating full activity or some restriction in strenuous activities.
• Have a heart function measurement of 50% or higher.

Exclusion Criteria

• Currently receiving other cancer treatments or have taken investigational drugs within 28 days before starting the study treatment.
• Have active or untreated hepatitis B or C, or chronic liver disease.
• Have significant heart problems or risks, such as heart failure, recent heart issues, abnormal heart rhythms, or poorly controlled high blood pressure.
• Have significant electrolyte imbalances or a family history of sudden unexplained death or long QT syndrome.
• Are taking medications or herbal supplements that strongly affect certain liver enzymes or are on specific blood thinners.