110 | wetenschapsdag 2023 Best Abstract Sessie 2 Auteurs A.K.E van Hemert, A.A van Loevezijn, M.S.P.D. Baas, M.P.M Stokkel, E Groen, C.E Loo, G.S Sonke, N.S Russell, F.H van Duijnhoven, M.J.T.F.D Vrancken Peeters Abstract titel Tailoring axillary treatment in lymph node positive breast cancer patients is associated with excellent oncologic outcome: 5-year recurrence free and overall survival in >400 patients undergoing the MARI protocol Background Axillary lymph node staging techniques after primary systemic therapy (PST) show low false negative rates. This led to an increased use of tailored axillary treatment, including omission of axillary lymph node dissection (ALND). However, robust data on oncologic outcomes following tailored axillary treatment after PST are lacking. Here, we present the five-year results of node positive (cN+) breast cancer patients treated according to the MARI (Marking Axillary lymph nodes with Radioactive Iodine seeds )-protocol. Methods We prospectively enrolled cN+ breast cancer patients who underwent axillary treatment according to the MARI-protocol between 2014 and 2019. Clinical nodal stage was assessed by FDG-PET/CT. Patients with cN<4 and pathologic complete response of the MARI node (MARI-pCR) did not receive further axillary treatment. Those with cN≥4 and MARI-non-pCR received ALND plus radiotherapy (RT). All other patients received RT alone. Primary endpoint was axillary recurrence-free survival (aRFS). Secondary endpoints were overall recurrence-free survival (RFS) and overall survival (OS). Results 411 patients were included: 201 (49%) with HR+/HER2- breast cancer; 69 (17%) HR+/HER2+; 55 (13%) HR-/HER2+ and 86 (21%) patients with triple negative (TN) disease. PET-CT identified 262 of 411 (55%) patients as having cN<4 of whom 92 (35%) with MARI-pCR. 149 of 411 patients had cN≥4 of whom 71 (48%) had a MARI-pCR. According to protocol, 22% (n=92) patients received no further axillary treatment, 59% (n=241) patients received RT and 19 % (n=78) patients underwent ALND plus RT. Median follow-up was 58 months (IQR 45 – 76). Five-year aRFS was 91% (N = 14, 95% CI 88 – 94). Overall RFS (75%; 95% CI 65 – 86) and OS (87%; 95% CI 80 – 96) was the worst in patients who underwent ALND plus RT. Conclusion Tailored axillary treatment in cN+ breast cancer patients by using the MARI protocol after PST is associated with an excellent fiveyear outcome.
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