Axillary lymph node dissection in node-positive breast cancer: are ten nodes adequate and when is enough, enough?

PURPOSE: National guidelines define adequate axillary lymph node dissections as those yielding ≥ 10 lymph nodes (LNs). We aimed to identify the optimal LN yield among node-positive patients.
METHODS: Using the National Cancer Data Base (2010-2015), we categorized node-positive patients as follows: (1) neoadjuvant chemotherapy (NAC, cN1-3 or ypN1mi-3) or (2) upfront surgery (pN1-3). A restricted cubic splines model was used to estimate LN retrieval thresholds associated with change in overall survival (OS).
RESULTS: 129,685 patients were identified: 21.2% NAC, 78.8% upfront surgery. Low, moderate, and high retrieval thresholds were estimated to be 1-6, 7-21, and > 21 LNs (upfront surgery), and 1-7, 8-22, and > 22 LNs (NAC). In an adjusted model, high versus low LN yield was associated with greater receipt of adjuvant chemotherapy (upfront surgery OR 1.96, p < 0.001) and greater use of adjuvant radiation (upfront surgery OR 1.08, p = 0.02; NAC OR 1.23, p = 0.002). After adjustment, high versus low LN retrieval was associated with improved OS (upfront surgery HR 0.86, p < 0.001; NAC HR 0.77, p < 0.001). Worse OS was associated with retrieving fewer LNs, likely as a result of an under-staged axilla and missed opportunity for adjuvant therapy, while better OS was independently associated with retrieval of up to approximately 20 LNs, after which survival did not improve.
CONCLUSION: In node-positive breast cancer, the number of nodes retrieved is significantly associated with an increased positive nodal count and greater use of adjuvant therapy. Removal of approximately 20 LNs may improve survival by both more accurate nodal staging and increased adjuvant therapy use.