Abstract OT2-01-01: Observational study of axilla treatment for breast cancer patients with 1 to 3 positive micrometastases or macrometastases in sentinel lymph nodes

[Background] Axilla surgery in node-positive breast cancer is dramatically changing from axillary lymph node dissection (ALND) to sentinel node biopsy (SNB). From the results of ACOSOG Z0011, IBCSG23-01 and AMAROS trials, adjuvant therapy and regional node irradiation could reduce regional lymph node recurrence for sentinel node-positive breast cancer patients. However, optimal indication of SNB alone remains uncertain. Trial design: To evaluate the outcome of sentinel node-positive breast cancer patients, the Japanese Society for Sentinel Node Navigation Surgery (SNNS) conducted a prospective cohort study in 2013 (UMIN000011782, Jpn J Clin Oncol, p.876-9, 2014). [Eligibility criteria] For eligible patients, SNB was performed or scheduled after 1 January 2012. Then 1 to 3 positive micrometastases or macrometastases in sentinel lymph nodes are confirmed by histological or molecular diagnosis. Primary chemotherapy before or after SNB is also acceptable for registration. [Specific aims] The primary endpoint is the 5-year recurrence rate of regional lymph node in patients treated with SNB alone. The secondary endpoint is the 5-year overall survival rate of this cohort. Patients treated with SNB followed by ALND are also registered simultaneously to compare the prognosis. The propensity score matching (PSM) is used to make the distributions of baseline risk factors comparable. [Statistical method] Based on an estimated recurrence rate of 5% at 5 years among patients treated with SNB alone, 240 patients are needed to give a 80% power to reject the null hypothesis that the recurrence rate is 10% with a one-sided type I error rate of 2.5%. If we consider that some patients will be lost to follow-up or become ineligible, a total of 250 patients will be needed to comprise the sample. [Present accrual] Eight hundred and eighty patients who underwent SNB alone or SNB followed by ALND were registered from 27 participating institutes between 2013 and 2016. Data cleaning is being performed. Patient9s background and PSM will be reported. Citation Format: Imoto S, Saito Oba M, Masuda N, Nagashima T, Wada N, Takashima T, Kitada M, Kawada M, Hayashida T, Taguchi T, Aihara T, Miura D, Toh U, Yoshida M, Sugae S, Yoneyama K, Matsumoto H, Jinno H, Sakamoto J. Observational study of axilla treatment for breast cancer patients with 1 to 3 positive micrometastases or macrometastases in sentinel lymph nodes [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-01-01.