Abstract P2-08-04: Prediction of distant recurrence by EndoPredict in patients with estrogen receptor-positive, HER2-negative breast cancer who received adjuvant endocrine therapy plus chemotherapy (ET+C) or endocrine therapy alone (ET)

Background: EndoPredict (EPclin) is a validated prognostic test combining expression of 12 cancer-related genes for breast cancer patients with estrogen receptor (ER) positive, HER2-negative disease who received 5 years of endocrine therapy (Buus et al., 2017; Dubsky et al. 2012) and for women who received chemotherapy (Martin et al., 2014). Here, we determine the EPclin and 10-year distant recurrence free interval (DRFI) rates for patients who received adjuvant endocrine therapy plus chemotherapy (ET+C) or endocrine therapy alone (ET) using data from five large clinical trials. Methods: A total of 3746 women with ER-positive, HER2-negative disease were included in this analysis. 2630 patients received 5 years of ET alone (ABCSG-6/8, TransATAC) and 1116 patients received ET+C (GEICAM 2003-02/9906). EPclin incorporates tumor size and nodal status and accounts for different EPClin scores between ET+C and ET alone cohorts. The primary objective was to evaluate the 10-year DRFI rates as a continuous function of EPclin separately for patients in ET+C and ET. Secondary objectives included assessing the difference in the prognostic ability of EPclin between ET+C and ET overall (years 0-10) and for specific follow-up periods (years 0-5 and years 5-10). The primary endpoint was DRFI and the secondary endpoint was breast cancer free interval (BCFI). Cox proportional hazard models were used to estimate 10-year DRFI rates and to assess the prognostic information provided by EPclin. Results: All of the women on ET alone and 49% of those on ET+C were postmenopausal. Women who received ET+C had more node positive disease, more poorly differentiated tumours, and higher EPclin scores than those who received ET alone. Women who received ET+C had significantly smaller increases in 10-year DRFI rates with increasing EPclin score than those receiving ET alone (Table). EPclin was highly prognostic for DRFI in all women who received ET alone (HR=2.79 (2.49-3.13), P Conclusion: In our results from a non-randomized analysis, we observed significantly smaller increases in 10-year DRFI rates with increasing EPclin scores for women who received ET+C compared to those who received ET alone. Our indirect comparisons suggest that a high EPclin score can predict chemotherapy benefit in women with ER-positive, HER2-negative disease. 10-year DRFI risks (%) (95% CI) according to EPclin score for patients who received ET+C versus ET alone. ET+CETEPclin10-year DR risk (%)10-year DR risk (%)11.1% (0.5-1.7)1.0% (0.6-1.4)22.5% (1.5-3.5)2.8% (2.1-3.5)35.7% (4.1-7.2)7.6% (6.4-8.8)412.4% (10.1-14.6)19.8% (17.6-22.0)525.8% (22.0-29.5)46.1% (40.2-51.4) Citation Format: Sestak I, Martin M, Dubsky P, Rojo F, Cuzick J, Filipits M, Ruiz A, Buus R, Hlauschek D, Rodriguez-Lescure A, Dowsett M, Gnant M. Prediction of distant recurrence by EndoPredict in patients with estrogen receptor-positive, HER2-negative breast cancer who received adjuvant endocrine therapy plus chemotherapy (ET+C) or endocrine therapy alone (ET) [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 P2-08-04.