Collectively, the expression profiling data following conditional OPN knockdown indicated an up-regulation of genes related to apoptosis (GOS2, IGFBP1), down-regulation of genes correlated with angiogenesis (RRM2) or tumor-cell adhesion (PVRL3), decrease of an osteolytic metastasis-associated gene (IL11), and up-regulation of a gene which counteracts uPA and is related to good prognosis in breast cancer patients (SERPINB2). This evidence concerns the gene SPP1 and breast cancer.