Abstract GS4-01: Radiotherapy or surgery of the axilla after a positive sentinel node in breast cancer patients: 10 year follow up results of the EORTC AMAROS trial (EORTC 10981/22023)

Background: Sentinel node biopsy (SNB) is standard in assessing axillary lymph node status in patients with clinically node-negative breast cancer. The 5-year analysis of AMAROS trial showed that if locoregional treatment is advised after a tumor-positive axillary SNB, axillary radiotherapy (ART) is a reasonable alternative for an axillary lymph node dissection (ALND) with less side effects, though follow up was relatively short. Here we present the 10-year follow up data. Methods: From February 2001 to April 2010, patients with primary breast cancer stage cT1-2N0M0 were enrolled in the EORTC phase III non-inferiority AMAROS trial by 34 European sites. Patients were randomized between ALND and ART in case of a tumor-positive SNB. The primary endpoint, axillary recurrence rate (AxR) is now assessed at 10 years in the ITT population using Fine and Gray cumulative incidence method with deaths as competing risks, as well as secondary endpoints: overall survival (OS), distant metastasis free survival (DMFS), second primaries (including cancers other than breast cancers and contralateral DCIS) and locoregional recurrences (LRR). Little extra information beyond 5 years was available concerning Quality of Life and morbidity. Data collection is still ongoing and will be presented later. Results:Of the 4806 patients entered, 1425 patients had a tumor-positive SNB: 744 in the ALND-arm and 681 in the ART-arm, 60% with a macrometastasis. Both treatment-arms achieved a median 10-year follow-up and were comparable regarding age, tumor size, grade, tumor type and adjuvant systemic treatment. In the group who had ALND, the 5-year AxR was 0.41% (95%CI: 0.00;0.88) (4/744) and the 10-year AxR was 0.93% (95%CI:0.18;1.68) (7/744). In the group who had ART, the 5-year AxR was 1.04% (95%CI: 0.27;1.81) (7/681) and the 10-year AxR was 1.82% (95%CI: 0.74;2.94) (11/681) (HR 1.71, 95%CI: 0.67;4.39, p = 0.37). Sensitivity analysis, considering deaths and distant recurrences as competing risks, revealed consistent results. There were no significant differences between treatment arms regarding OS (ALND: 84.6% (95%CI: 81.5;87.1), ART: 81.4% (95%CI: 77.9;84.4), HR 1.17, 95%CI: 0.89;1.52, p= 0.26) and DMFS (ALND: 81.7% (95%CI: 78.5;84.4), ART: 78.2% (95%CI: 74.6;81.3), HR 1.18, 95%CI: 0.92;1.50, p=0.19). Cumulative incidence estimates of 10-year LRR are 3.59% (95%CI: 2.12;5.06) (ALND) versus 4.07% (95%CI: 2.49;5.65) (ART) (p= 0.69). More second primaries were observed after ART: 75/681 (21 contralateral breast) as compared to ALND: 57/744 (11 contralateral breast) (p = 0.035). All results are consistent in the per protocol analysis of patients with a tumor-positive SNB. Conclusion: Axillary recurrence after 10 years in patients with a tumor-positive SNB who were treated with ART is extremely rare and not significantly different from patients who were treated with ALND. OS, DMFS and locoregional control are also comparable. Second primaries including contralateral breast cancers are more frequently encountered after ART, but the difference is still low in absolute numbers. Thus, ART is a safe treatment for breast cancer patients with a tumor-positive SNB. Citation Format: Rutgers EJ, Donker M, Poncet C, Straver ME, Meijnen P, van de Velde CJ, Mansel RE, Blanken C, Orzalesi L, Klinkenbijl JH, van der Mijle HC, Veltkamp SC, van 9t Riet M, Albregts M, Marinelli A, Rijna H, Tobon Morales R, Snoj M, Bundred N, Chauvet MP, Merkus JW, Petignat P, Schinagl DA, Coens C, Peric A, Bogaerts J, van Tienhoven G. Radiotherapy or surgery of the axilla after a positive sentinel node in breast cancer patients: 10 year follow up results of the EORTC AMAROS trial (EORTC 10981/22023) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS4-01.