Discordance between Breast and Axillary Responses After Neoadjuvant Chemotherapy in Triple-Negative Breast Cancer:...

Our objective was to investigate breast-axillary pathological response discordance after neoadjuvant chemotherapy (NACT) in triple-negative breast cancer (TNBC).

We retrospectively analyzed 651 patients with TNBC who received NACT followed by surgery. Four composite response patterns were defined by breast pathological complete response (BpCR) and nodal pathological complete response (NpCR). Logistic regression assessed factors associated with residual axillary disease in patients with BpCR and with NpCR in patients without BpCR. Era-stratified analyses compared 2014-2019 and 2020-2024.

Discordance occurred in 30.6% (199/651). Among patients with BpCR, 17.8% had residual axillary disease. Higher initial clinical nodal (cN) stage was associated with residual axillary disease (all P < 0.05), whereas immunotherapy was associated with lower odds (odds ratio [OR] 0.259; 95% confidence interval [CI] 0.080-0.842; P = 0.025). Human epidermal growth factor receptor 2 (HER2)-low status showed a marginal association (OR 2.599; 95% CI 1.013-6.668; P = 0.047). Era-stratified analyses supported the cN-stage association; immunotherapy was not reliably estimable in 2014-2019 and was favorable but non-significant in 2020-2024. Among patients without BpCR, 34.8% experienced NpCR; initial cN stage was the only independent factor associated with NpCR (all P < 0.001), with an NpCR rate of 80.9% in cN0 disease.

Breast-axillary discordance is common after NACT in TNBC. Initial axillary burden was the most consistent factor associated with axillary response. HER2-low may be an exploratory marker, whereas the immunotherapy association requires cautious interpretation. These findings may inform future axillary de-escalation trials.