Response–Guided Axillary Treatment of Node-Positive Breast Cancer: The MARI Protocol

The quest to de-escalate therapy for breast cancer has prompted tailored axillary lymph node dissection, modified radiation therapy (RT) protocols, and fewer mastectomies; but do these less-intense treatments raise recurrence risk, thereby compromising survival? Investigators in the Netherlands pursued the “marking the axillary lymph node with a radioactive seed” (MARI) protocol in patients with operable breast cancer and node-positive disease. Those who attained a pathologic complete response (pCR) in the MARI node following primary systemic treatment (PST) received no further axillary treatment, while those with residual disease received RT including the axilla. Patients undergoing breast-conserving surgery (BCS) received RT to the breast. Those with residual nodal disease at surgery received RT to the breast or chest wall as well as the axilla. The primary outcome was axillary recurrence rate; secondary outcomes included invasive disease-free survival (iDFS) and overall survival (OS).

Key Results

In all, 350 patients (median age, 49 years) were enrolled from 2014–2021 with median follow-up of 49 months. Among 135 patients, pCR of the MARI node was confirmed, whereas 215 had residual disease. Most patients (65%) underwent BCS. In patients with pCR in the MARI node, the axillary recurrence rate was 0.7%, 5-year iDFS was 93%, and OS was 98%, while among patients with residual disease in the MARI node, axillary recurrence occurred in 2.3%, with iDFS of 82% and OS of 93%.