Abstract PO3-06-02: Ten years axillary recurrence and survival after omission of axillary lymph node dissection in breast cancer patients with micrometastases or isolated tumor cells in the sentinel node: A Danish national register study

Abstract Background: Until 2012, breast cancer patients with micrometastases (pN1mi) or isolated tumor cells (pN0(i)) in the sentinel node (SN) received axillary lymph node dissection (ALND). ALND is associated with lymphedema, paresthesia, functional impairment, and pain. In 2012, national Danish guidelines for patients with pN1mi and pN0(i) were changed reflecting several randomized clinical trials showing non-inferior prognosis when ALND was omitted. Since 2012, appr. 450 Danish breast cancer patients have been spared ALND each year. Development of axillary recurrence(AR) from minimal metastatic disease left in the axilla may take longer than experienced after macrometastatic disease. Hence, long-term follow-up is needed to evaluate the safety of omitting ALND for patients with pN1mi and pN0(i). Therefore, we aimed to investigate these outcomes with 10 years of follow-up. Methods: In this national register-based study, we included all women with primary breast cancer surgery between 01.01.2008 and 31.12.2021, who had pN1mi and pN0(i) in the SN. Women treated between 01.01.2008-31.12.2011 had received ALND, while in women treated between 01.01.2012 and 31.12.202,1 ALND was omitted. The two groups were compared with SN-negative patients (pN0) without ALND. The primary outcome was AR, and the secondary outcome was overall survival (OS). Information on surgery, nodal status, and recurrence were retrieved from the national Danish breast cancer group (DBCG) database. The definitions of pN1mi, pN0(i) and pN0 were according to AJCC, 8TH edition. We analyzed patient- and tumor characteristics with descriptive statistics, χ2 and Fisher exact test. The cumulative incidence of AR was calculated. OS was estimated using the Kaplan-Meier method and compared with a log-rank test. The effect of ALND was estimated with a Cox proportional hazards model, adjusting for age at operation, histology, malignancy grade, hormone receptor, HER2 status, and whether they received adjuvant systemic treatment or radiation therapy. With all statistical analysis, a two-tailed α-level of 0.05 was used. Results: 22,790 patients were included in the study. Overall,14.3% had pN1mi, 8.6% had pN0(i) and 77.1% had pN0. Of pN1mi or pN0(i) patients, 1490 had an ALND; 1227 patients with pN1mi and 263 patients with pN0(i). In 3737 patients ALND was omitted: 2036 with pN1mi and 1701 with pN0(i). Regarding the primary outcome, 1.1% of patients with pN1mi or pN0(i) had an AR, while 0.5% of the pN0 patients had AR. Analyzing patients with pN1mi or pN0(i) with or without ALND, 0.2% and 1.5%, respectively, had an AR. In subanalysis of patients with pN1mi with or without ALND, 0.2% and 1.8%, respectively, had an AR. In a subanalysis of patients with pN0(i), no patients with pN0(i) and ALND had an AR, while 1.1% of patients with pN0(i) had an AR when ALND was omitted. OS after 10 years of follow-up for the group of patients with pN1mi or pN0(i) was 81.5%; 83.7% for patients with and 79.12% for patients without ALND. For pN0 patients without ALND OS was 82%. This difference between the three groups was statistically significant(p 0,01). However, when adjusting for risk factors, there was no statistically significant difference in OS between the patients with pN1mi or pN0(i) with and without ALND (p=0.6). Likewise, no statistically significant difference was found in OS, when looking at the subgroups of pN1mi with or without ALND (p=0.5) and pN0(i) with and without ALND(p=0.41). Conclusion: In this large register-based nationwide study we found a slightly higher rate of AR after 10 years of follow-up in breast cancer patients with micrometastases or isolated tumor cells in the SN if ALND was omitted. However, the axillary recurrence rate was low ( 2%), and after adjusting for other risk factors the increased recurrence rate did not affect OS. These results confirm the safety of omitting ALND in these patients. Citation Format: Riazan Hawaz-ali, Frederikke Munck, Tove Tvedskov, Niels Kroman. Ten years axillary recurrence and survival after omission of axillary lymph node dissection in breast cancer patients with micrometastases or isolated tumor cells in the sentinel node: A Danish national register study abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-02.