What are the current guidelines for post‑mastectomy radiotherapy in patients with an inadequate axillary lymph‑node dissection (fewer than ten nodes removed)?

PMRT Guidelines for Inadequate Axillary Dissection

When fewer than 10 lymph nodes are removed during axillary dissection, the decision to administer post-mastectomy radiotherapy (PMRT) should be based on the number of positive nodes identified rather than the total number of nodes examined, with PMRT strongly recommended for any patient with ≥4 positive nodes regardless of adequacy of dissection. 1

Defining Adequate Axillary Dissection

• Traditional level I and II axillary lymph node dissection requires removal of at least 10 lymph nodes for accurate staging 1, 2
• The EBCTCG meta-analysis defined adequate axillary dissection as: inclusion in a protocol requiring at least an anatomic level I to II dissection, a median of 10 nodes examined in the study population, or individual patient data showing 10 or more recovered nodes 1
• Dissection should include tissue inferior to the axillary vein from the latissimus dorsi muscle laterally to the medial border of the pectoralis minor muscle (level I/II) 1, 2

PMRT Recommendations Based on Nodal Status (Regardless of Number Examined)

Four or More Positive Nodes

• PMRT is mandatory for all patients with ≥4 positive axillary lymph nodes, even with inadequate dissection (fewer than 10 nodes removed) 1
• The 10-year locoregional failure rate without PMRT is 31.5% versus 13.6% with PMRT in patients receiving systemic therapy 1
• PMRT reduces 20-year breast cancer mortality from 78.0% to 70.0% (relative risk 0.89) 1
• Supraclavicular field irradiation should be included in all patients with ≥4 positive nodes 1

One to Three Positive Nodes with Inadequate Dissection

• For patients with 1-3 positive nodes and fewer than 10 nodes examined, PMRT should be strongly considered, as the true nodal burden remains uncertain 1
• The EBCTCG meta-analysis showed PMRT reduces 10-year locoregional failure from 21.0% to 4.3% in patients with 1-3 positive nodes who underwent adequate dissection 1
• With inadequate sampling (0-7 uninvolved nodes examined), the 10-year chest wall recurrence risk exceeds 15%, supporting PMRT consideration 3

Risk Stratification for Inadequate Dissection Cases

When fewer than 10 nodes are removed, the following high-risk features warrant PMRT even with 1-3 positive nodes:

• Age <40 years (10-year chest wall recurrence 16.1% without PMRT) 3
• Lymphovascular invasion present 3
• 0-7 uninvolved nodes examined (indicating inadequate sampling with 10-year chest wall recurrence >15%) 3
• ≥3 positive sentinel lymph nodes even with negative completion ALND (10-year locoregional failure 74.7% vs 96.7% for <3 positive SLNs) 4
• T3 tumors with any positive nodes 1

Technical Specifications for PMRT

• Chest wall irradiation is mandatory when PMRT is administered 1
• Both internal mammary nodes (IMNs) and supraclavicular-axillary apical nodes should generally be treated in addition to the chest wall when PMRT is used for patients with positive axillary lymph nodes 1
• Full axillary radiotherapy should not be given routinely to patients who have undergone any level of axillary dissection (even if inadequate) to minimize lymphedema risk 1

Critical Decision-Making Algorithm

Step 1: Determine number of positive nodes identified

• If ≥4 positive → PMRT indicated (proceed to Step 3)
• If 1-3 positive → proceed to Step 2
• If 0 positive → PMRT generally not indicated

Step 2: For 1-3 positive nodes, assess adequacy of dissection and risk factors

• If <10 nodes examined AND any high-risk feature present (age <40, LVI, 0-7 uninvolved nodes, ≥3 positive SLNs, T3 tumor) → PMRT strongly recommended 3, 4
• If <10 nodes examined but no high-risk features → PMRT should be discussed in multidisciplinary setting 1
• If ≥10 nodes examined → use standard PMRT guidelines for 1-3 positive nodes 1

Step 3: Define radiation fields

• Chest wall (mandatory) 1
• Supraclavicular-axillary apical nodes 1
• Internal mammary nodes 1
• Avoid full axillary field if any dissection performed 1

Common Pitfalls to Avoid

• Do not withhold PMRT in patients with ≥4 positive nodes simply because fewer than 10 nodes were examined - the absolute number of positive nodes determines benefit, not the adequacy of sampling 1
• Do not assume low nodal burden when fewer than 10 nodes are examined with 1-3 positive - inadequate sampling may underestimate true disease burden 3
• Do not irradiate the entire dissected axilla after any level of axillary dissection - this substantially increases lymphedema risk without proven benefit 1
• Do not omit regional nodal irradiation (supraclavicular and IMN fields) when PMRT is indicated - chest wall alone is insufficient 1