Omitting axillary lymph node dissection in breast cancer patients with extensive nodal disease and excellent response to primary systemic therapy using the MARI protocol

Purpose: Axillary lymph node staging techniques after primary systemic therapy (PST) show low false negative rates, stimulating the omission of axillary lymph node dissection (ALND). Breast cancer patients with extensive nodal disease are underreported in studies on response-guided axillary treatment. In this study, we present the oncologic outcome of breast cancer patients with ≥4 involved axillary lymph nodes treated according to the MARI-protocol. Methods: This prospective single arm registration study included breast cancer patients with extensive nodal disease defined as ≥4 involved axillary lymph nodes on FDG-PET/CT pre-PST between July 2014 and December 2021. After PST, the marked (MARI) lymph node was excised. Patients with a pathologic complete response (pCR) of the MARI node (ypN0) received locoregional radiation treatment (RT). In patients with residual disease of the MARI node (ypN+), ALND was performed followed by RT. Primary endpoint was axillary recurrence rate. Secondary endpoints were invasive disease-free survival (DFS) and overall survival (OS). Results: In total, 218 patients were registered of which 39 % of patients also had extra-axillary nodal disease. Median (IQR) age was 50 (42–57) years. After PST 47 % of patients (103/218) had ypN0, whereas 53 % of patients (115/218) had ypN+. After a median follow up of 44 (26–62) months, axillary recurrence rate was 2.9 % (n = 3) in the ypN0 group and 3.5 % (n = 4) in the ypN + group. Five-year invasive DFS and OS were respectively 89 % (95 % CI 83 %–96 %) and 95 % (95 % CI 91 %–99 %) in ypN0 patients. Conclusion: Omission of ALND after PST in breast cancer patients with extensive nodal involvement who achieve pCR of the MARI node is associated with excellent five-year oncologic outcome.