SMAD1 and breast cancer: To provide clinical evidence of the role of the FOXF2/BMP/SMAD axis in breast cancer bone metastasis, we analyzed the expression of BMP4 and SMAD1 in primary breast cancer tissues that developed bone-only metastasis (n = 61) or metastases in other distant organs with or without bone metastases (n = 36) based on the GSE2034_GSE2603 data set; we also analyzed the expression of these genes in metastatic tissues in bone (n = 18) and in other distant organs (n = 47) based on the GSE14020 data set.