Treatment Options for HER2-Positive Metastatic Breast Cancer

Primary Second-Line Recommendation

The European Society for Medical Oncology recommends T-DM1 as the alternative second-line treatment when trastuzumab deruxtecan is not available or contraindicated, with established efficacy after progression on taxane and trastuzumab-based regimens 1, 2
T-DM1 achieved a median progression-free survival of 9.6 months versus 6.4 months with lapatinib plus capecitabine in the EMILIA trial, with a hazard ratio for death of 0.62 3

For patients with brain metastases, the American Society of Clinical Oncology prioritizes tucatinib plus capecitabine plus trastuzumab as an alternative second-line option 1, 2

After second-line therapy, the National Comprehensive Cancer Network recommends considering tucatinib plus capecitabine plus trastuzumab (Level I, A evidence) if T-DM1 was used second-line 1, 2
The European Society for Medical Oncology recommends lapatinib plus capecitabine (Level I, C evidence) if T-DM1 was used second-line 1, 2

For patients with HR-positive/HER2-positive disease, the American Society of Clinical Oncology recommends endocrine therapy plus lapatinib (Level II, B evidence) after exhausting standard HER2-targeted therapies with chemotherapy 1, 2
The National Comprehensive Cancer Network recommends continuing HER2-targeted therapy as the backbone even when adding endocrine therapy 4

The European Society for Medical Oncology states that never discontinuing all HER2-targeted therapy when disease progresses is a critical treatment principle 1, 2, 4
Continued anti-HER2-based therapy is the current clinical standard for patients with HER2-positive tumors 1, 2

The Journal of the National Comprehensive Cancer Network states that T-DM1 has a generally better tolerated toxicity profile than lapatinib plus capecitabine 3
The Cancer Treatment Reviews journal notes that tucatinib combination can cause elevated aminotransferases (16.5% grade ≥3 when combined with T-DM1) 5

The American Society of Clinical Oncology advises against sequencing a tyrosine kinase inhibitor after another TKI without intervening therapy 1, 2
The European Society for Medical Oncology recommends not using single-agent endocrine therapy without HER2-targeted therapy in HER2-positive disease unless cardiac contraindications exist 1
The National Comprehensive Cancer Network states that stopping HER2-targeted therapy at disease progression should be avoided; continue with different chemotherapy or treatment partners 1, 2, 4

The American Society of Clinical Oncology recommends trastuzumab deruxtecan (T-DXd) as the preferred second-line therapy for patients with HER2-positive metastatic breast cancer who have progressed on first-line Abraxane, pertuzumab, and trastuzumab, demonstrating superior progression-free survival and overall survival compared to all other options 6, 7
Trastuzumab deruxtecan (T-DXd) 5.4 mg/kg IV every 3 weeks should be offered as the standard second-line treatment, based on the DESTINY-Breast03 trial, which showed superior overall survival outcomes 6, 7

The National Comprehensive Cancer Network recommends continuing HER2-targeted therapy beyond disease progression, as this is a fundamental principle supported by multiple trials demonstrating benefit from ongoing HER2 blockade 8

The American Society of Clinical Oncology recommends tucatinib plus trastuzumab plus capecitabine as the preferred third-line option for patients who received T-DXd in second-line and progress, based on a study showing median PFS of 7.8 months versus 5.6 months with placebo combination (HR 0.54; P<0.001) 7
Trastuzumab with different chemotherapy partners (vinorelbine, other taxanes, capecitabine) is a recommended alternative third-line option 8, 9

For patients with active brain metastases, tucatinib-based combination is the preferred option at any line after first-line therapy, and local therapies (surgical resection, stereotactic radiotherapy) should be considered first if eligible 7
For patients with hormone receptor-positive disease, HER2-targeted therapy plus chemotherapy remains the preferred approach, with strongest evidence 6

The American Society of Clinical Oncology recommends continuing HER2-targeted therapy until disease progression or unacceptable toxicity, and not stopping when chemotherapy is discontinued 6
T-DXd is contraindicated in patients with pre-existing interstitial lung disease, and monitoring is required for interstitial lung disease/pneumonitis, elevated aminotransferases, diarrhea, and palmar-plantar erythrodysesthesia with tucatinib combinations, as well as cardiac dysfunction with all trastuzumab-based regimens 6, 7, 8