Histological assessment of treatment effect in lymph node-positive breast cancer after neoadjuvant chemotherapy

Neoadjuvant chemotherapy (NACT) is becoming the standard of care for lymph node (LN)-positive breast cancers. Residual disease in the breast and LN serves as a critical prognostic indicator and guides adjuvant therapy. The histological patterns of LN treatment response (TE) vary significantly, and criteria for evaluating TE remain underdeveloped.

We analysed 114 clinical node-positive cases that underwent NACT, reviewed post-NACT LN TE, and correlated them with clinicopathological characteristics. TE was identifiable in 77% of all cases and 92% of post-NACT nodal conversion cases. The histological patterns of TE include a special "rounded" pattern of fibrosis (86%), LN architectural irregularity with aggregates of histocytes, foamy macrophages, and haemosiderin deposition (54%), and fine-needle aspirated site changes (34%). Microscopically identifiable TE, except fibrosis, diminishes as the interval between LN sampling and surgery increases. Specifically, among the four cases that failed to identify TE in the nodal conversion group, 3 (75%) surgeries were performed >6 months after initial LN sampling. In cases with multiple clinically suspicious LNs, only one of which was sampled pre-NACT, recognition of a specific fibrosis pattern allowed identification of TE in unsampled LNs (9 cases, 18%) post-NACT, contributing to an accurate post-NACT assessment. Post-NACT nodal-positive cases correlated with poor outcomes.

Given the paradigm shift of increased NACT, evaluation of TE in LN is critically important. Awareness of the histological features of TE is crucial for LN assessment to ensure accurate nodal removal and guide post-NACT clinical management for best patient care.