Exploring the molecular difference among breast cancer subtypes is of crucial importance in understanding its heterogeneity and seeking its effective clinical treatment. For this, several layers of information including immunohistochemical markers and a variety of high-throughput genomics approaches have been intensively used. Here we have explored the intrinsic differences among breast cancer subgroups defined by immunohistochemical expression (IHC) of hormone receptors ER and PR as well as human epidermal growth factor receptor 2 (HER2) using the mRNA and miRNA expression profiles of 115 tumors. A core basal group was further defined by epidermal growth factor receptor and cytokeratin 5/6 IHC expression and compared to triple negative group. A set of differentially expressed genes including 1015 mRNAs and 69 miRNAs was found to distinguish tumor subtypes whose generality was demonstrated using two independent data sets. The network was explored for each subtype and biomass synthesis signaling was found to play an important role in the core basal subgroup. This study contributes to elucidating the intrinsic relations among breast cancer subgroups defined by ER, PR and HER2 expression via integrating mRNA and miRNA expression. The results can avail functional studies of breast cancer with translational potential for clinical use.