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Gene Expression and Benefit of Chemotherapy in Women With Node-Negative, Estrogen Receptor–Positive Breast Cancer
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2023
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The relationship between the 21‑gene recurrence score (RS) and chemotherapy benefit in node‑negative, estrogen‑receptor‑positive breast cancer was previously unknown. The study aimed to determine whether the RS predicts the magnitude of benefit from adjuvant chemotherapy in this patient population. RS values were obtained from tumors of patients in the NSABP B20 trial, and Cox proportional hazards models tested the interaction between chemotherapy and RS. A significant interaction was observed in 651 patients, with high‑RS (≥31) patients showing a large benefit (relative risk 0.26) and low‑RS (<18) patients deriving minimal benefit, demonstrating that RS predicts chemotherapy benefit magnitude.
Purpose The 21-gene recurrence score (RS) assay quantifies the likelihood of distant recurrence in women with estrogen receptor–positive, lymph node–negative breast cancer treated with adjuvant tamoxifen. The relationship between the RS and chemotherapy benefit is not known. Methods The RS was measured in tumors from the tamoxifen-treated and tamoxifen plus chemotherapy–treated patients in the National Surgical Adjuvant Breast and Bowel Project (NSABP) B20 trial. Cox proportional hazards models were utilized to test for interaction between chemotherapy treatment and the RS. Results A total of 651 patients were assessable (227 randomly assigned to tamoxifen and 424 randomly assigned to tamoxifen plus chemotherapy). The test for interaction between chemotherapy treatment and RS was statistically significant (P = .038). Patients with high-RS (≥ 31) tumors (ie, high risk of recurrence) had a large benefit from chemotherapy (relative risk, 0.26; 95% CI, 0.13 to 0.53; absolute decrease in 10-year distant recurrence rate: mean, 27.6%; SE, 8.0%). Patients with low-RS (< 18) tumors derived minimal, if any, benefit from chemotherapy treatment (relative risk, 1.31; 95% CI, 0.46 to 3.78; absolute decrease in distant recurrence rate at 10 years: mean, −1.1%; SE, 2.2%). Patients with intermediate-RS tumors did not appear to have a large benefit, but the uncertainty in the estimate can not exclude a clinically important benefit. Conclusion The RS assay not only quantifies the likelihood of breast cancer recurrence in women with node-negative, estrogen receptor–positive breast cancer, but also predicts the magnitude of chemotherapy benefit.