Bone morphogenetic protein 7 (BMP-7) is an important regulator of cell development and differentiation of various organs. Tumorigenesis and tumor progression are also strongly associated with changes of the fate of cells which are highly differentiated in healthy tissues. Therefore, we studied the role of BMP-7 in breast cancer cell lines and in breast tumor tissue samples. BMP-7 is expressed in various cell lines, but in a cell line specific manner. The breast cancer cell lines MCF-7 and SK-BR-3 showed BMP-7 expression on the mRNA level. In T-47D we were not able to detect BMP-7 on the mRNA but on the protein level. Additionally, epidermal growth factor (EGF), a stimulator of proliferation, was not able to enhance BMP-7 expression on the transcriptional level. These findings are in contrast to the EGF-dependent regulation of BMP-6, indicating a differential regulation of these closely related TGF-beta members. In order to confirm the data obtained from cell cultures, we analyzed normal breast tissue and tumor tissue samples from 170 invasive ductal carcinomas of the breast by immunohistochemistry. We found BMP-7 expression in normal breast tissue in the end buds, but not in the ductus lactiferus. BMP-7 protein was detected in all 170 tumor samples. Comparing BMP-7 levels with histopathological parameters, we could not show a correlation of BMP-7 and the proliferation index nor with erbB receptors. But the expression of BMP-7 was highly correlated with estrogen receptor levels (p< or=0.01) and progesterone receptor levels (p< or =0.01) which are important markers for breast cancer prognosis and therapy.