ConclusionsTaken together, the results imply that miRsyn is a promising framework for identifying miRNA synergism, and it could enhance the understanding of miRNA synergism in breast cancer. Keywords miRNA -miRNA synergistic network -miRNA synergistic module -Multiple intervention causal inference -Breast cancer Background MicroRNAs (miRNAs) are a class of short non-coding RNAs with ~23 nucleotides (nts) in length. They play an important regulatory role at the post-transcriptional level by targeting messenger RNAs (mRNAs) for degradation or translation repression [1].Previous studies have demonstrated that miRNAs play a crucial role in regulating gene expression involved in diverse biological processes, including cell proliferation, cell death, cell apoptosis and human cancers [2][3][4]. Generally, the relationships between miRNAs and their target genes are not one-to-one but many-to-many, indicating cooperative regulation of miRNAs. The co-regulation of miRNAs has been accepted and confirmed by cross-linking and immunoprecipitation technologies, and may be related to human complex diseases [5]. Therefore, studying miRNA synergism can greatly help to understand the synergistic regulation mechanism of miRNAs in human diseases.Until now, a number of computational methods have been proposed to identify miRNA synergism. These methods can be divided into three different categories: (1) sequence-based [6-8], (2) correlation-based [9][10][11][12][13][14], and (3) causality-based [15]. In the first category, the sequence data mainly includes putative miRNA-target interactions and protein-protein interactions (PPIs). For each candidate miRNA-