Which ancillary lymph nodes are associated with breast cancer?

Lymph Nodes Associated with Breast Cancer Metastasis

Breast cancer primarily metastasizes to axillary lymph nodes (levels I, II, and III), internal mammary lymph nodes, infraclavicular lymph nodes, and supraclavicular lymph nodes. 1

Axillary Lymph Node Levels

The axillary lymph nodes are anatomically divided into three levels:

• Level I (low axilla): Lymph nodes lateral to the lateral border of the pectoralis minor muscle
• Level II (mid axilla): Lymph nodes between the medial and lateral borders of the pectoralis minor muscle
• Level III (apical axilla/infraclavicular): Lymph nodes medial to the medial border of the pectoralis minor muscle, extending up to the clavicle 2

Regional Lymph Node Metastasis Patterns

Primary Metastatic Pathways

1. Axillary lymph nodes - Most common site of regional metastasis

   • Typically follows a sequential pattern from Level I → Level II → Level III
   • Level I and II involvement is most common 1

2. Internal mammary lymph nodes

   • May be involved with or without axillary node involvement
   • More common in medial and central breast tumors 1

3. Infraclavicular (Level III axillary) lymph nodes

   • Associated with more advanced disease
   • Usually occurs after Level I and II involvement 1

4. Supraclavicular lymph nodes

   • Indicates more advanced disease (classified as N3c)
   • Associated with poorer prognosis 1

Clinical Significance of Nodal Involvement

The extent of lymph node involvement significantly impacts staging, prognosis, and treatment decisions:

• pN1: 1-3 axillary nodes and/or internal mammary nodes with micrometastases
• pN2: 4-9 axillary nodes or clinically detected internal mammary nodes without axillary involvement
• pN3: ≥10 axillary nodes, infraclavicular nodes, internal mammary nodes with positive axillary nodes, or supraclavicular nodes 1

Evaluation of Axillary Lymph Nodes

Accurate assessment of axillary lymph node status is crucial for:

• Determining disease stage
• Guiding surgical management
• Planning adjuvant therapy
• Predicting prognosis 3

Sentinel lymph node biopsy (SLNB) has become the standard approach for initial axillary staging in clinically node-negative patients, allowing for less invasive assessment with high accuracy 4.

Important Clinical Considerations

• Micrometastases (>0.2 mm but ≤2.0 mm) and isolated tumor cells (≤0.2 mm) have different prognostic implications than macrometastases (>2.0 mm) 1
• The number of involved nodes is a critical prognostic factor
• Extracapsular extension of tumor in lymph nodes indicates more aggressive disease
• Post-neoadjuvant chemotherapy nodal status requires careful assessment, as it may differ from pre-treatment status 1

Pitfalls to Avoid

• Relying solely on clinical examination for nodal assessment (has limited sensitivity)
• Overlooking internal mammary node involvement, especially in medial/central tumors
• Failing to consider skip metastases (involvement of higher level nodes without lower level involvement)
• Underestimating the significance of micrometastases in treatment planning 3, 4