In this study, we quantified 249 mature micro-RNA (miRNA) transcripts in estrogen receptor-positive (ER ⁺ ) primary breast tumors of patients with lymph node-negative (LNN) disease to identify miRNAs associated with metastatic capability. In addition, the prognostic value of the candidate miRNAs was determined in ER ⁻ /LNN breast cancer. Unsupervised analysis in a prescreening set of 38 patients identified three subgroups predominantly driven by three miRNA signatures: an ER-driven luminal B-associated miRNA signature, a stromal miRNA signature, and an overexpressed miRNA cluster located on chromosome 19q23, but these intrinsic miRNA signatures were not associated with tumor aggressiveness. Supervised analysis in the initial subset and subsequent analysis in additional tumors significantly linked four miRNAs ( miR-7 , miR-128a , miR-210 , and miR-516–3p ) to ER ⁺ /LNN breast cancer aggressiveness ( n = 147) and one miRNA ( miR-210 ) to metastatic capability in ER ⁻ /LNN breast cancer ( n = 114) and in the clinically important triple-negative subgroup ( n = 69) (all P < 0.05). Bioinformatic analysis coupled miR-210 to hypoxia/VEGF signaling, miR-7 and miR-516–3p to cell cycle progression and chromosomal instability, and miR-128a to cytokine signaling. In conclusion, our work connects four miRNAs to breast cancer progression and to several distinct biological processes involved therein.