Abstract PS6-27: Secondary invasive breast events (SIBE) among patients with oncotype DX recurrence scores (RS) 26-30 and >31: Results from a large oncotype database

Background: Oncotype RS is a 21-gene assay used to predict the likelihood of distant recurrence and benefit of chemotherapy in patients with lymph node negative (LN-), hormone positive (HR+) breast cancer (BC). The Oncotype RS is used to identify patients who may be spared chemotherapy in the adjuvant setting without adverse impact on survival or secondary invasive breast events (SIBE). Results of the TAILORx trial (Sparano et al, 2018) provided evidence that chemotherapy can likely be spared for most patients with oncotype RS 31) to determine the benefit of chemotherapy among these groups. Methods:We identified 887 patients with early-stage, HR+ BC treated between 2006-2018. Among these patients, 515 had treatment and follow-up data available for SIBE analysis. Median follow-up for SIBE was 62 months with 41 SIBE (8%) including both LN+ and LN- patients. When stratified by RS using conservative cutoffs (Sparano et al, 2018): low risk ( 26), 5 year rates of SIBE were 4%, 6% and 16% respectively. The Kaplan Meier method was used to estimate the time to SIBE distributions overall and among different RS groups with the log rank test used to compare distributions between groups. Results: Among 887 patients, 616 (69%) were post-menopausal. A total of 654 (74%) patients had surgical management, of which 226 underwent mastectomy (35%) and 428 underwent lumpectomy (65%). Among the 630 patients who received adjuvant therapy, 14 (2%) received chemotherapy alone, 143 (23%) received a combination of chemotherapy/endocrine therapy and 473 (75%) received endocrine therapy alone. Twenty-four patients (3%) refused one or more recommended therapies. Three hundred fourteen patients (50%) also received radiation therapy. Rates of chemotherapy administration were 8% among low RS, 16% among intermediate RS and 82% among high RS patients (73% for RS 26-30 and 90% for RS >31). One-hundred eighty six of 887 patients were missing chemotherapy administration data as they were likely treated at another center. Patients with treatment data available and adequate follow up were included in the SIBE analysis (n=515). Among the 27 LN- patients with RS 26-30, twenty (74%) received chemotherapy and the remaining seven (26%) did not. The five year rate of SIBE was 25% among patients who received chemotherapy and 33% among those who did not receive chemotherapy; p=0.5489. Among the 23 LN negative patients with RS >31, twenty-one (91%) patients received chemotherapy and the remaining two (9%) did not. The five year rate of SIBE was 0% in both patients who received chemotherapy and in patients who did not receive chemotherapy; p-value not estimable in this subgroup due to no SIBE in either group. Conclusion: In this large oncotype database, there was no statistically significant difference in SIBE for patients with higher genomic risk (RS 26-30 and >31) whether or not they received chemotherapy. This data was limited by small numbers of patients in these sub-groups. More aggressive endocrine therapy with ovarian suppression has become an alternative option to spare chemotherapy in intermediate risk patients (RS 11-25). This approach may be useful among patients with even higher risk oncotype scores. Prospective randomized studies may be useful to determine utility of chemotherapy among patients with RS >26. Citation Format: Brittney S Zimmerman, Krystal Cascetta, Natalie Berger, Serena Tharakan, Kelly Suchman, Julia Blanter, Erin Moshier, Meng Ru, Shabnam Jaffer, Amy Tiersten. Secondary invasive breast events (SIBE) among patients with oncotype DX recurrence scores (RS) 26-30 and >31: Results from a large oncotype database [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-27.