SPP1 and breast cancer: This is consistent with previous studies pointing to a role for increased OPN deposition in the pathologies underlying mineralization and bone metastasis of breast cancer cells.44, 45 In addition, Runx2 and OSX (osteogenesis‐specific transcription factors) are expressed during osteoblastic differentiation of BMSCs.46, 47 Runx2 is required for differentiation of mesenchymal cells into pre‐osteoblasts.