Background: Accurate prediction of distant metastasis (DM) in early stage ER+/HER2- breast cancer (BC) patients is vital to avoid over/under-treatment with adjuvant chemotherapy (CT). The OncotypeDX Recurrence Score (RS) is a widely used tool to assist clinical decision-making for CT. The StemPrintER Risk Score (SPRS) is an alternative genomic predictor based on the biology of cancer stem cells that predicts recurrence risk in ER+/HER2- BCs (Pece S. et al., EBioMedicine 2019). Here, we analyze the prognostic value of SPRS in the TransATAC cohort of post-menopausal ER+/HER2- BC patients, and compare the prognostic information provided by SPRS and RS for 10-year risk of DM. Methods: The likelihood χ² (LRχ²) and Kaplan-Meier survival analyses were used to assess prognostic information provided by SPRS, RS and the clinical treatment score (CTS) in 818 TransATAC patients treated with anastrozole or tamoxifen for 5 years. Comparative analyses were made for DM risk over the 10-year follow-up, as well as in the early (0-5 years) or late (5-10 years) interval, according to nodal status. Results: Used as a continuous variable, SPRS was an independent predictor of DM in years 0-10 among all patients when adjusted for clinical parameters as expressed by the CTS [HR=1.43 (1.18-1.73), P<0.0001], as well as in node-negative [HR=1.51 (1.17-1.94), P=0.001] but not node-positive (N1-3) patients [HR=1.29 (0.95-1.75), P=0.11]. A predefined SPRS cut-off was used to stratify patients into low vs. high risk groups [LOW: N=454, 10-year DM rate=5.8%; HIGH: N=364, 10-year DM rate=21.9%; HR_{HIGH vs. LOW}=2.96 (1.85-4.73); P<0.0001]. SPRS outperformed RS in providing prognostic information for 10-year DM risk (SPRS: HR=1.79, P<0.0001, LRχ²=33.4; RS: HR=1.52, P<0.0001, LRχ²=22.1), with even greater differences in late DM prediction in N0 patients. SPRS also provided more prognostic information than RS to CTS (ΔLRχ²: SPRS+CTS vs. CTS= 14.9; RS+CTS vs. CTS= 9.7). Conclusions: In ER+/HER2- TransATAC BC patients, SPRS was highly prognostic for DM and was superior to RS in providing additional prognostic information to conventional clinicopathological parameters.