First-Line Systemic Therapy for HER2-Positive Metastatic Breast Cancer with Brain Metastases

Standard First-Line Regimen

• The European Society for Medical Oncology (ESMO) guidelines designate trastuzumab, pertuzumab, and a taxane as the preferred first-line therapy with the highest evidence grade (MCBS 1A) for patients who are candidates for chemotherapy, irrespective of brain metastases status 1
• The American Society of Clinical Oncology (ASCO) guidelines recommend offering HER2-targeted therapy according to standard algorithms for HER2-positive metastatic breast cancer, even in the presence of brain metastases 3, 4
• Trastuzumab plus pertuzumab plus a taxane should be offered as first-line therapy for at least 6 cycles, followed by maintenance with trastuzumab and pertuzumab (with or without endocrine therapy if hormone receptor-positive) 1

Critical Considerations for Brain Metastases

• Patients with asymptomatic or stable brain metastases should receive standard first-line trastuzumab-pertuzumab-taxane therapy 3, 4
• Patients whose systemic disease is progressive at the time of brain metastasis diagnosis should follow standard HER2-positive metastatic breast cancer treatment algorithms 3, 4
• The presence of brain metastases alone does not change the first-line systemic therapy choice 1

Treatment Algorithm for Newly Diagnosed Patients

• Patients with 1-4 brain metastases should be considered for stereotactic radiosurgery (SRS) prior to or concurrent with systemic therapy 6
• Patients with symptomatic brain metastases or significant mass effect require local therapy (surgery or radiation) before or alongside systemic treatment 3, 4
• Patients with asymptomatic, small brain metastases (<2-3 cm) may proceed directly to systemic therapy with close monitoring 7, 8

Maintenance Therapy

• Continue trastuzumab plus pertuzumab indefinitely until progression or unacceptable toxicity 1
• Add endocrine therapy to trastuzumab-pertuzumab maintenance if hormone receptor-positive (ESMO MCBS 1A) 1

Special Scenarios

• If metastatic recurrence occurs ≥12 months after completing adjuvant trastuzumab (without pertuzumab), proceed with standard first-line trastuzumab-pertuzumab-taxane 1
• If recurrence occurs within 6-12 months of adjuvant trastuzumab-pertuzumab, consider moving directly to second-line therapy (T-DXd preferred) 1
• If recurrence occurs <6 months after adjuvant trastuzumab-pertuzumab, treat according to second-line recommendations 1