["To identify the individual genes or gene modules that lead to the OncoptypeDx 21-gene recurrence score's reduced performance after 5 years and thereby identify indices of residual risk that may guide selection of patients for extended adjuvant therapy.", 'We conducted a retrospective assessment of the relationship between (i) the individual genes and gene modules of the Recurrence Score and (ii) early (0-5 years) and late (5-10 years) recurrence rates in 1,125 postmenopausal patients with primary estrogen receptor-positive breast cancer treated with anastrozole or tamoxifen in the Arimidex, Tamoxifen, Alone or Combined (ATAC) randomized clinical trial.', 'In the HER2-negative population (n = 1,009), estimates of recurrence risk were similar between years 0-5 and 5-10 for proliferation and invasion modules but markedly different for the estrogen module and genes within it (all split at the median): for low estrogen module, annual recurrence rates were similar across the two time windows (2.06% vs. 2.46%, respectively); for high estrogen module, annual rates were 1.14% versus 2.72%, respectively (P interaction = 0.004). Estrogen receptor transcript levels showed inverse prediction across the time windows: HR, 0.88 (0.73-1.07) and 1.19 (0.99-1.43), respectively (P interaction = 0.03). Similar time-, module-, and estrogen-dependent relationships were seen for distant recurrence.'] Does estrogen Receptor Expression in 21-Gene Recurrence Score predict Increased Late Recurrence for Estrogen-Positive/HER2-Negative Breast Cancer?