Factors associated with nodal pathologic complete response among breast cancer patients treated with neoadjuvant chemotherapy: results of CALGB 40601 (HER2+) and 40603 (triple-negative) (Alliance)

BACKGROUND: De-escalation of axillary surgery after neoadjuvant chemotherapy (NAC) requires careful patient selection. We sought to determine predictors of nodal pathologic complete response (ypN0) among patients treated on CALGB 40601 or 40603, which tested NAC regimens in HER2+ and triple-negative breast cancer (TNBC), respectively. METHODS: 760 patients with stage II-III HER2+ or TNBC were analyzed. Those who had axillary surgery before NAC (n=122), or who had missing pre-treatment clinical nodal status (cN) (n=58) or ypN status (n=41) were excluded. The proportion of patients with ypN0 disease was estimated for those with and without breast pathologic complete response (pCR) according to pre-treatment nodal status. RESULTS: In 539 patients, the overall ypN0 rate was 76.3% (411/539) – 93.2% (245/263) in patients with breast pCR and 60.1% (166/276) with residual breast disease (RD) (P