What is the recommended treatment approach for patients with breast micrometastasis?

Treatment of Breast Micrometastasis

For patients with breast micrometastasis (≤2 mm axillary lymph node metastases), axillary lymph node dissection is not required, and systemic adjuvant therapy should be guided by hormone receptor status and tumor characteristics. 1

Surgical Management

• Sentinel lymph node biopsy alone is sufficient for micrometastases without completion axillary lymph node dissection. 1
• The IBCSG 23-01 trial definitively demonstrated no difference in 5-year disease-free survival (84.4% vs 87.8%) or overall survival (97.6% vs 97.5%) between patients with micrometastases who underwent axillary dissection versus those who did not. 1
• Regional recurrence rates were <1% in both groups, confirming the safety of omitting axillary dissection. 1
• This applies to both breast-conserving therapy and mastectomy patients (9% of the trial cohort underwent mastectomy). 1

Systemic Adjuvant Treatment Algorithm

For Hormone Receptor-Positive, HER2-Negative Disease:

Node-negative or micrometastasis only (pN1mi):

• Adjuvant endocrine therapy alone is recommended (Category 2B). 1
• Consider adding chemotherapy followed by endocrine therapy for higher-risk features, though this remains Category 2B evidence. 1

If genomic testing (e.g., Oncotype DX) is available:

• Low recurrence score (<18): Endocrine therapy alone 1
• Intermediate score (18-30): Endocrine therapy OR chemotherapy followed by endocrine therapy 1
• High score (≥31): Chemotherapy plus endocrine therapy 1

For Hormone Receptor-Negative Disease:

• Adjuvant chemotherapy is recommended for micrometastatic disease. 1
• Treat as you would for a new primary with curative intent including appropriate adjuvant modalities. 1

For HER2-Positive Disease:

• Consider pertuzumab-containing regimens for patients with micrometastatic (≥N1) disease. 1
• Trastuzumab-based therapy should be incorporated with non-anthracycline chemotherapy. 1

Critical Pitfalls to Avoid

Do not perform routine axillary lymph node dissection for micrometastases. The evidence is clear that this provides no survival benefit and increases morbidity. 1

Do not withhold systemic therapy based solely on micrometastatic status. While the nodal burden is minimal, micrometastases indicate systemic risk and warrant appropriate adjuvant treatment based on tumor biology. 1

Ensure proper pathological assessment. Micrometastases are defined as tumor deposits >0.2 mm but ≤2.0 mm. Isolated tumor cells (≤0.2 mm) are classified differently and may not require the same treatment approach. 1

Sequencing of Therapy

• Chemotherapy and endocrine therapy should be given sequentially, with endocrine therapy following chemotherapy. 1
• Sequential or concurrent endocrine therapy with radiation therapy is acceptable. 1

Special Considerations

For postmenopausal patients with hormone receptor-positive disease and 1-3 involved nodes (including micrometastases):

• Consider adjuvant bisphosphonate therapy to improve outcomes. 1

Radiation therapy:

• Whole breast radiation therapy remains standard after breast-conserving surgery regardless of micrometastatic status. 1

The key distinction with micrometastatic disease is that it represents a favorable prognostic subset where less aggressive surgical management (omitting completion axillary dissection) is appropriate, while systemic therapy decisions should still be based on tumor biology and overall risk assessment rather than nodal status alone. 1