A Clinical Trial to Compare the Effectiveness and Safety of RO7771950 in Combination with Trastuzumab and Capecitabine, Versus Tucatinib in Combination with Trastuzumab and Capecitabine, in People with Locally Advanced or Metastatic Breast Cancer that is HER2-Positive

You likely can't join if

• Treatment with investigational therapy within 28 days prior to initiation of study treatment
• Concurrent anti-cancer treatment. Concurrent use of hormonal therapy for noncancer-related conditions (i.e., hormone replacement therapy for hypothyroidism) or for ovarian function suppression is allowed. Ongoing or planned bisphosphonate treatment is allowed in participants with bone metastases.
• Based on screening brain MRI, any of the following criteria for participants with brain metastasis: – Progressive neurologic impairment or increased intracranial pressure, which is symptomatic (including nausea, vomiting, blurred vision, headache, epilepsy, etc.) – Any intracranial lesion that is expected to require immediate local therapy. After local therapy, the participant can be re-screened for the protocol. – Requirement for systemic corticosteroids for management of CNS symptoms at a total daily dose of 2 mg of dexamethasone (or equivalent). A stable or tapering dose of 2 mg is permitted. – Requirement for anti-epileptic medication for seizure control, with the exception of stable-dose levetiracetam
• Participants who meet one of the following cardiac criteria: – Congestive heart failure (CHF; New York Heart Association [NYHA] functional classification) of 2 – Clinically significant peripheral arterial disease, like coronary artery disease, hypertrophic cardiomyopathy, or dilated cardiomyopathy – Abnormalities in the ECG measurements: such as first-degree heart block, second degree heart block, third-degree heart block, prolonged PR interval: 0.20 s – Any clinically significant supraventricular arrhythmia or ventricular arrhythmia requiring treatment or intervention – Unstable angina – Myocardial infarction within the past 6 months – Percutaneous transluminal coronary angioplasty/stenting, coronary artery bypass graft within 6 months of the first dose of the study treatment – QT interval corrected through use of Fridericia's formula (QTcF) prolongation (470 ms for women and 450 ms for men), a known history of QTcF prolongation or Torsade de Pointes; or is on drugs that are required for existing medical conditions and that may result in QT prolongation (e.g., anti-arrhythmic drugs) – Poorly controlled hypertension (e.g., systolic  180 mm Hg or diastolic  100 mmHg) – History of ventricular dysrhythmias or risk factors for ventricular dysrhythmias such as structural heart disease (e.g., severe left ventricular systolic dysfunction [LVSD], left ventricular hypertrophy) – Coronary heart disease (symptomatic or with ischemia demonstrated by diagnostic testing) – Clinically significant electrolyte abnormalities (e.g., hypokalemia, hypomagnesemia, hypocalcemia), or family history of sudden unexplained death or long QT syndrome
• Participants with known active and/or untreated hepatitis B or hepatitis C or chronic liver disease are ineligible. Participants with a diagnosis of hepatitis B or C that has been treated and cleared (viral genetic test should fulfil the local laboratory definition for "cleared"), and normal liver function are eligible to participate in the study if the other eligibility parameters are met. Virologic testing should be conducted according to local institutional practices