Abstract P1-13-07: Effect of adjuvant chemotherapy for patients with ER-positive/HER2-negative breast cancer assessed by the propensity score matching: Significance of nuclear grade and nodal status

Abstract

Purpose: Although a survival benefit with chemotherapy (CT) is obtained over all among patients with estrogen receptor-positive (ER+) breast cancer, the degree of benefit differs among the subtypes. The 21-gene Recurrence Score assay is a validated prognostic/predictive tool for early ER+ breast cancer. However, genomic assays have not been approved in Japan and most other countries, except in some developed countries. Based on the St. Gallen 2015, 1-3 positive nodes are not an absolute indication for CT among patients with ER+/HER2-negative breast cancer. In contrast, it is better for CT to be performed except for low-risk groups, based on genomic tests according to the St. Gallen 2017. In fact, no prospective study has proven the survival benefit of CT specifically for luminal-A breast cancer. Therefore, we analyzed the survival benefit of CT for ER+/HER2-negative breast cancer by propensity score matching (PSM). Patients and methods: Between 2000 and 2015, 895patients with stage I-III ER+/HER2-negative breast cancer who had underwent surgery in our hospital were examined. Patients with bilateral breast cancer, ER<10%, and preoperative treatment were excluded. The primary end point was the 5-year recurrence-free survival (RFS) and overall survival (OS) in patients matched by propensity score that estimated by a logistic regression model that included factors likely to influence the decision of whether or not to administer CT (tumor size, nuclear grade [NG], progesterone receptor status and nodal status). Results: In the entire cohort, the median age was 59 (28-95) years; 223 patients (24.9%) were node positive and 126 patients (14.1%)had NG3 disease. Overall, all patients received endocrine therapy, and 24.1% received additional CT. After a median follow-up of 68.8 months, the 5-year RFS rate was 94.3% in CT-untreated patients (non-CT group) and 90.1% in CT-treated patients (CT group; hazard ratio [HR] for recurrence, 1.47; 95% confidence interval [CI], 0.90 -2.33; p=0.106). The 5-year OS rate was 97.5% in the non-CT group and 95.6% in the CT group (HR for death, 1.80; 95% CI, 0.99-3.21; p=0.047). Using PSM, 236 patients were selected (1:1 matching between non-CT and CT groups). After matching, the 5-year RFS rate was higher in the CT group than in the non-CT group (96.8% vs. 82.7%; HR for recurrence, 0.29; 95% CI, 0.11-0.68; p=0.003), and the 5-year OS rate was higher in the CT group than in the non-CT group (100% vs. 91.9%; HR for death, 0.06; 95% CI, 0.003-0.35; p<0.001). Among PSM patients, with node-negative/NG3 and 1-3 node positive/NG2 disease, the 5-year RFS rate was significantly higher in the CT group than in the non-CT group (p=0.041 and p=0.006, respectively). Conclusion: No significant benefit of CT was observed when considering the entire cohort because of the treatment bias. When clinical and tumor features were matched by propensity score, the addition of CT significantly improved both RFS and OS of ER+/HER2-negative breast cancer patients, especially for patients with node- negative/NG3 and 1-3 node positive/NG2 disease. Citation Format: Tanaka N, Ogura K, Kamimura M, Hattori A, Inoue H, Yukawa H, Sakaguchi S, Matsuoka A, Kodera A, Hirano A. Effect of adjuvant chemotherapy for patients with ER-positive/HER2-negative breast cancer assessed by the propensity score matching: Significance of nuclear grade and nodal status [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 P1-13-07.