Related to tumor and metastasis development, the following points especially emphasize the role of GC action in breast cancer: (1) GCs seem to act as both tumor suppressor and tumor promoter in breast tissue in a cell-type specific manner and in a context-dependent way; (2) in the majority of breast cancer cases, tumor development and growth are initially steroid hormone dependent and involve GR crosstalk with other hormone receptors; (3) GCs are routinely administered as adjuvant treatment for the side effects of conventional chemotherapy. This evidence concerns the gene NR4A1 and breast cancer.