Likelihood of relapse according to RFRS group. Kaplan-Meier survival analysis shows a significant difference in relapse-free survival for low-, intermediate-, and high-risk groups as defined by: (A) the full-gene-set model on training data (n = 572, P = 3.95E-11); (B) the eight-gene-set model on independent test data (n = 286, P = 2.84E-05); (C) the eight-gene-set model on independent NKI data (n = 89, P = 0.004); (D) the 17-gene-set model on independent METABRIC data (n = 315, P <1.99E-04). Note, for panel A, the risk scores and corresponding groups for samples used in classifier training (n = 325) were assigned from internal OOB cross-validation. Only those patients not used in initial training (training data without 10-year follow-up; test data) were assigned a risk score and group by de novo classification. Significance between risk groups was determined by Kaplan-Meier log rank test (with test for linear trend).