Nodal involvement in patients with small, clinically node-negative HER2-positive breast cancer after staging with FDG-PET/CT and neoadjuvant systemic therapy

Guidelines recommend systemic therapy for stage I HER2+ breast cancer (BC). Neoadjuvant systemic treatment (NAST) allows response-guided adjuvant treatment. However, prior to NAST only clinical nodal staging is available, risking undertreatment if ypN+ is observed. Here, we aim to evaluate the impact of FDG-PET/CT and NAST on nodal disease status in patients with small, node-negative HER2+ BC. This retrospective study included patients with small (≤3 cm), clinically node-negative HER2+ BC diagnosed between 2011 and 2023. Primary outcome was the proportion of patients with nodal disease on final pathology after upfront surgery or NAST followed by surgery with or without FDG-PET/CT. Patients received either paclitaxel + trastuzumab (PT) or a more extensive regimen. Of the 370 included patients, 183 underwent FDG-PET/CT, detecting regional or distant metastases in 14 patients (7.7 %). Among 356 patients with cN0 disease, 44.1 % (n = 157/356) had upfront surgery, with only 3 % (5/157) having an FDG-PET/CT. The remaining 55.9 % (199/356) started with NAST, with 82 % (n = 164/199) having an FDG-PET/CT. Among patients treated with NAST, 36 % received PT. Nodal involvement on pathology was seen in 19.1 % (n = 29/152) after upfront surgery without FDG-PET/CT and 6.1 % (10/164) after NAST combined with FDG-PET/CT. After NAST, 58 % had a pCR (PT: 49 %, other: 63 %). Nodal involvement on final pathology was seen in 6.9 % after PT and in 5.5 % after more extensive regimen. The proportion of patients with ypN + after NAST combined with FDG-PET/CT was only 6.1 %. Neoadjuvant treatment can be a safe treatment strategy for patients with stage I HER2+ BC. •Population: small (≤3 cm), clinically node negative, HER2-positive breast cancer.•Nodal involvement after neoadjuvant systemic treatment and FDG-PET/CT was 6.1 %.•Nodal involvement after upfront surgery without FDG-PET/CT was 19.1 %.