LBA18Clinical outcomes by chemotherapy regimen in patients with RS 26-100 in TAILORx

Abstract Background The recurrence score (RS) based on the 21-gene breast cancer assay predicts chemotherapy benefit if it is high and a low risk of recurrence in the absence of chemotherapy if it is low. There is little information from prospective clinical trials, however, regarding outcomes for patients with a high RS treated with chemotherapy regimens including taxanes and/or anthracyclines. Methods Women with hormone-receptor-positive, HER2-negative, axillary-node-negative breast cancer and a high RS of 26-100 were assigned to receive endocrine therapy plus a chemotherapy regimen selected by the treating physician. Results Among the 9719 eligible women, 1389 (14%) had a RS of 26-100.The most common chemotherapy regimens included docetaxel/cyclophosphamide in 589 (42%), an anthracycline without a taxane in 334 (24%), an anthracycline and taxane in 244 (18%), cyclophosphamide/methotrexate/5-FU in 52 (4%), other regimens in 81 (6%), and no chemotherapy in 89 (6%). The estimated rates of freedom from recurrence of breast cancer at a distant site were 93.0% (standard error [SE]+0.8%) at 5 years and 86.8% (SE + 1.7%) at 9 years. In contrast, the projected rates of freedom from distant recurrence in this population if treated with endocrine therapy alone was estimated to be 78.8% (SE ± 14.0%) at 5 years and 65.4% (SE ± 10.4%) at 9 years when estimating outcomes based on the treatment effect of chemotherapy noted in the HER2-negative cohort of the B20 trial. Five-year rates of freedom from distant recurrence ranged from 92.3% to 95.5% for all chemotherapy regimens with the exception of CMF (88.5%). Conclusions The estimated rate of freedom from distant recurrence in women with a RS of 26-100 treated with a variety of adjuvant taxane and/or anthracycline-containing chemotherapy regimens plus endocrine therapy in the prospective TAILORx trial was 93% at 5 years, an outcome better than expected with endocrine therapy alone in this population. Clinical trial identification NCT00310180. Legal entity responsible for the study ECOG-ACRIN Cancer Research Group. Funding USA National Cancer Institute, Genomic Health. Disclosure All authors have declared no conflicts of interest.