Study on Tucatinib or Placebo with Trastuzumab and Pertuzumab for Advanced HER2+ Breast Cancer

Inclusion Criteria

• Have HER2-positive breast cancer confirmed by specific medical guidelines.
• Have cancer that cannot be surgically removed or has spread to other parts of the body.
• If the cancer has returned after previous treatment, there must be at least a 6-month gap since the last treatment with trastuzumab and pertuzumab.
• Have completed 4-8 cycles of initial therapy with trastuzumab, pertuzumab, and taxane without disease progression.
• Have known hormone receptor status, which can be positive or negative.
• Have a performance status score of 0 or 1, indicating full activity or some restriction in strenuous activities.
• Based on a brain MRI, participants may have:
  • No brain metastases
  • Untreated, asymptomatic brain metastases not needing immediate treatment
  • Previously treated, asymptomatic brain metastases that have not progressed since treatment

Exclusion Criteria

• Have previously been treated with any HER2 or EGFR-targeting tyrosine kinase inhibitors, except for neratinib under specific conditions.
• Cannot undergo a contrast-enhanced MRI of the brain.
• Based on brain MRI and clinical assessment, participants may not have:
  • Symptomatic brain metastases after local treatment
  • Progression of brain metastases since starting initial therapy
  • Ongoing use of systemic corticosteroids above a certain dose
  • Untreated brain lesions in risky locations
  • Known or suspected leptomeningeal disease
  • Poorly controlled seizures or other persistent neurological symptoms