Recent studies show that the expression levels of the oncogenic miR-17/92 cluster in triple-negative breast cancer is three times higher than other subtypes.29, 30 Here, we analyzed miR-20a expression from TCGA miRNA-seq data set; miR-20a expression was markedly higher in breast cancer tissues (Figure 1a). We identified miR-20a expression signature predictive of estrogen receptor (ER), progesterone receptor (PR) or human epidermal growth factor receptor 2 (HER2). The TCGA samples were subdivided into clinically the relevant subgroups: ER negative (n=109), ER positive (n=384), PR negative (n=164), PR positive (n=328), HER2 negative (n=411) or HER2 positive (n=71) based on immunohistochemical expression of hormone receptors. A significant upregulation of miR-20a expression was observed in ER-negative or PR-negative tumors (Supplementary Figure S1). Tumors with the triple-negative immunophenotyped account for up to 15% of breast cancer. Comparison of miR-20a levels between triple-negative breast cancers (n=82) and other subtypes (n=391) revealed that miR-20a is upregulated in triple-negative subtype (Figure 1b). These results demonstrate that miR-20a might be a potential diagnostic marker to distinguish triple-negative breast cancer from other subtypes.