ESR1 and breast cancer: To understand the crosstalk between expression pattens of Spp1 upstream factors, i.e., ERα and ERRα in breast cancer, analysis of RNAseq data from a total of 1075 human breast cancer samples revealed a higher co-expression of Esrra and Spp1 (70.4% of total tumors) compared to relatively lower co-expression of Esr1 and Spp1 (48.4% of total tumors).