# Axillary response and diagnostic accuracy of imaging modalities after neoadjuvant chemotherapy for breast cancer (retrospective single center study)

## TL;DR

This study examines how well imaging techniques detect remaining cancer in lymph nodes after chemotherapy for breast cancer patients.

## Contribution

The study identifies HER2 positivity and PR negativity as factors linked to better axillary response to chemotherapy.

## Key findings

- HER2-positive and PR-negative tumors showed higher axillary pathological complete response rates.
- PET-CT and ultrasound had high specificity but modest sensitivity for detecting residual axillary metastasis.
- Luminal A and B tumors responded less to chemotherapy compared to HER2-rich and triple-negative subtypes.

## Abstract

The optimal axillary approach after neoadjuvant chemotherapy (NACT) in patients with breast cancer (BC) remains controversial. In our study, we aimed to evaluate factors affecting axillary pathological complete response (pCR) in patients with biopsy-proven node-positive BC before NACT and to assess the diagnostic performance of imaging modalities in detecting residual axillary metastasis after NACT.

Our sample included 142 patients with T1–3, N1–2, M0 BC who were cytologically confirmed to have axillary metastasis by ultrasonography (USG), mammography (MG), magnetic resonance imaging (MRI), and 18F-FDG positron emission tomography–computed tomography (PET-CT) and who received NACT between 2020 and 2025. Patients showing clinical or radiologic complete response in the axilla underwent sentinel lymph node biopsy (SLNB). SLNB-positive patients subsequently underwent level I–II axillary dissection (AD). Pathological, molecular, and imaging findings of the patients were analyzed.

After NACT, 78 patients (54.9%) had no residual axillary metastasis. HER2 positivity and progesterone receptor (PR) negativity were significantly associated with axillary pCR (p < 0.05). Luminal A and B tumors demonstrated lower response rates to NACT, whereas HER2-rich and triple-negative subtypes showed higher axillary pCR rates (85.7% and 71.4%, respectively). Among imaging modalities, the specificity values were 91.2% and 84.6% for PET-CT and USG, respectively. Negative predictive values (NPV) were 74.02% and 76.52% for PET-CT and USG, respectively.

In PR-positive and HER2-negative tumors, the likelihood of axillary pCR is lower, and careful evaluation is warranted. USG and PET-CT may serve as a good guide for axillary lymph node assessment after NACT in patients with BC. However, given their modest sensitivity, imaging modalities should be considered complementary tools rather than substitutes for pathological axillary staging. Further prospective randomized trials are needed to define patient groups who may safely avoid axillary dissection after NACT.