Abstract P3-08-68: Application of 21-gene recurrence score in patients with T1-2, N0-1 ER-positive/HER2 negative breast cancer: Survival analysis in relation to clinical risk score
Authors: Bae Soong June , Ahn Sung Gwe , Park Soeun , Cha Chi Hwan , Kim Dooreh , Lee Janghee , Jeong Joon 
Published: March 2020

Abstract
Background: Incorporating 21-gene recurrence score (RS) into daily practice have saved chemotherapy in about more than two-third of ER(+)/HER2(-) patients. In those with node-positive disease, 21-gene RS showed a clinically meaningful benefit in terms of reducing chemotherapy. We investigated the rate of chemotherapy and a short-term clinical outcome in patients with T1-2, N0-1 ER(+)/HER2(-) breast cancer after we actively applied 21-gene RS in our daily practice.
Method: We identified T1-2, N0-1, ER(+)/HER2(-) breast cancer patients who underwent breast surgery followed by adjuvant treatment from January 2014 to December 2018. The clinical risk score (CRS) was defined as low and high based on histologic grade, tumor size, and nodal status as used in MINDACT trial. The rate of chemotherapy and survival outcomes were analyzed according to CRS and whether 21-gene RS was performed or not. Also, the patients were classified into 3 groups: Group A, endocrine alone without 21-gene RS; Group B, endocrine or chemo-endocrine guided by 21-gene RS; Group C, chemo-endo without 21-gene RS. In the patients between 2014 and 2016, we investigated the recurrence-free survival (RFS).
Results: In a total of 1,008 patients, there were 446 (44.2%) for group A, 352 (34.9%) for group B, and 210 (20.8%) for group C, showing that 21-gene RS was done in about one-third of all. The rate of high CRS was 18.2% (81 of 446) in the group A, 42.3% (149 of 352) in the group B, and 71.0% (149 of 210) in the group C (P&lt;0.001). In the low-CRS group, 36 (17.7%) of 203 patients with 21-gene RS received chemotherapy and 61 (14.3%) of 365 patients without 21-gene RS received chemotherapy (P=0.268). However, in the high-CRS group, 46 (30.9%) of 149 patients with 21-gene RS received chemotherapy although 149 (64.8%) of 230 patients without 21-gene RS received chemotherapy (P&lt;0.001). In the patients eligible for survival analyses, a median follow-up was 36 months. In women treated with endocrine alone, there were no difference of RFS between the patients with or without 21-gene RS (P=0.147). Also, the RFS did not differ between two groups with or without 21-gene RS, regardless of CRS (log-rank test, P=0.657 in the high-CRS group, and P=0.803 in the low-CRS group, respectively).
Conclusions: These results supported that the application of 21-gene RS reduced the rate of chemotherapy in N0-1 patients with high CRS. Further study with a long-term follow up is needed to clarify an oncologic safety of a reduced the chemo-endocrine rate brought by 21-gene RS in terms of survival outcomes.
Key words: breast neoplasm, adjuvant treatment, 21-gene recurrence score, chemotherapy
Citation Format: Soong June Bae, Sung Gwe Ahn, Soeun Park, Chi Hwan Cha, Dooreh Kim, Janghee Lee, Joon Jeong. Application of 21-gene recurrence score in patients with T1-2, N0-1 ER-positive/HER2 negative breast cancer: Survival analysis in relation to clinical risk score [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-08-68.