Abstract PO3-17-09: Outcome after the introduction of personalized treatment for axilla in patients with clinically node-negative early breast cancer

Abstract Background : After the results of ACOSOG Z0011 and AMAROS trials were reported, axillary treatment has been promoted to de-escalation. For clinically negative cases of axillary lymph node metastasis (cN0), axillary dissection (Ax) has been the standard treatment when sentinel lymph node (SN) metastasis is positive. In our hospital, for patients with cN0, if SN macro metastasis is positive, Ax or irradiation (RT) is selected after sufficient explanation to the patients. Five years have passed since the introduction of treatment selection for the axilla, we examined treatment outcomes retrospectively. Methods : The subjects were 1376 patients who underwent SN biopsy for primary breast cancer with cN0 at our hospital from October 2004 to December 2018 (median observation period 79 months). Cases who underwent preoperative chemotherapy were excluded. We have introduced the treatment choice system since December 2015, and compared prognosis (local recurrence, distant recurrence and breast cancer specific death) before and after introduction using the log-rank test. Results : There were 947 cases before introduction of treatment choice system (pre group) and 429 cases after introduction (post group). The median observation period for each group was 91 months and 41 months. The maximum observation period post group was 67 months, then we compared the number of events in patients with observation period less than 67 months in pre group. There was no significant difference between two groups (Pre/Post) in terms of age (p=0.52), menopausal status (p=0.90), invasion of primary lesion (p=0.19), biology and SN metastasis status (p=0.41). There were 54 patients (12.6%) in pre group and 135 (14.3%) patients in post group had positive sentinel lymph nodes. In post group, 33 patient (61.1%) were macrometastasis of SN, 28 of whom underwent Ax and 5 underwent RT. Local recurrence was 4 cases (1.7%) in pre group, 9 cases (2.1%) in post group (p=0.84), distant recurrence was 13 cases (5.6%) and 5 cases (1.2%) (p=0.0002), and breast cancer specific death was 8 cases (0.8%) and 1 case (0.2%) (p=0.0003), respectively. Discussion : There was no significant difference in local recurrence rate within 67 months, but were poor prognosis in pre introduction group for distant metastasis and breast cancer specific survival. In the results of this study, there was no significant difference in local recurrence, but the prognosis for distant recurrence and breast cancer-specific death was poor in the before introduction group. The median observation period in the post introduction group was 47 months, and late recurrence of ER-positive breast cancer occurs later. It is necessary to continue the study by extending period and accumulation cases. Conclusion : For cN0 cases, if the case is suitable, we introduced the treatment choice system that allows omitting Ax by performing radiotherapy in SN macrometastasis positive patients. After introduction, there was no increase in the relapse rate after introduction in the short term. Appropriate case selection allowed the safety introduction of individualizes treatment for axilla. Citation Format: Mai Tomiguchi, Kaori Hidaka, Lisa Goto-Yamaguchi, Ayako Kajiwara, Kanako Nishikido, Toko Inao, Yutaka Yamamoto. Outcome after the introduction of personalized treatment for axilla in patients with clinically node-negative early breast cancer 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 PO3-17-09.