Several studies reported that OPN expression is increased in bone tissues of chronic bone inflammatory diseases such as rheumatoid arthritis, periodontitis, and metastatic cancer in bone (Kido et al., 2001; Ohshima et al., 2002; Carlinfante et al., 2003; Kusuyama et al., 2017). This evidence concerns the gene SPP1 and metastatic malignant neoplasm.