# Impact of axillary disease extent defined by baseline 18F-FDG PET/CT on the accuracy of axillary surgical staging after neoadjuvant systemic therapy in clinically node-positive breast cancer

## TL;DR

This study shows that the extent of axillary disease seen on a PET/CT scan before treatment affects how accurately surgeons can stage breast cancer after therapy.

## Contribution

The study introduces a new way to assess the accuracy of surgical staging procedures based on baseline PET/CT findings in node-positive breast cancer patients.

## Key findings

- Staging procedures were more accurate when baseline axillary disease was limited (1-3 hypermetabolic nodes).
- When staging detected residual disease, the risk of remaining positive nodes was much higher with advanced baseline disease.
- SLNB or MARI detection of residual disease indicated a high risk of remaining disease regardless of baseline disease extent.

## Abstract

In clinically node-positive patients, sentinel lymph node biopsy (SLNB), marking axillary lymph node with radioactive iodine seed (MARI), and combined SLNB/MARI (RISAS-procedure) can replace axillary lymph node dissection (ALND) after neoadjuvant systemic therapy. Surgical staging outcome can be combined with baseline axillary disease on 18F-FDG PET/CT. This study assessed whether baseline axillary disease on 18F-FDG PET/CT affects the accuracy of staging-procedures. Second, when staging-procedures detected residual disease, it was assessed whether baseline axillary disease on 18F-FDG PET/CT affected the probability of remaining positive nodes at completion ALND (cALND).

Included were patients with baseline 18F-FDG PET/CT within the RISAStrial (NCT02800317). Patients underwent the RISAS-procedure followed by cALND. False negative rates were stratified by limited or advanced baseline axillary disease (1-3 vs. ≥4 hypermetabolic lymph nodes). When staging-procedures detected residual disease, the probability of remaining positive nodes at cALND was stratified by baseline axillary disease.

Of 185 patients, 116 had limited and 69 had advanced baseline axillary disease. Staging-procedures had higher accuracy in limited than advanced baseline axillary disease. When the RISAS-procedure detected residual disease, the probability of remaining positive nodes at cALND was lower in limited than advanced baseline axillary disease (44.9% vs. 91.5%,p < .001). When SLNB or MARI detected residual disease, the probability of remaining positive nodes at cALND was >88.4%, irrespective of baseline axillary disease.

Staging-procedures had higher accuracy in patients with limited than advanced axillary disease on baseline 18F-FDG PET/CT. When staging-procedures detected residual disease, the probability of remaining positive nodes at cALND remained high.

•Surgical staging was followed by completion axillary lymph node dissection.•Accuracy of surgical staging was higher with 1-3 hypermetabolic nodes at baseline.•Detection of disease at surgical staging indicated high risk of remaining disease.•Risk of disease after surgical staging is crucial to guide adjuvant treatment.

Surgical staging was followed by completion axillary lymph node dissection.

Accuracy of surgical staging was higher with 1-3 hypermetabolic nodes at baseline.

Detection of disease at surgical staging indicated high risk of remaining disease.

Risk of disease after surgical staging is crucial to guide adjuvant treatment.