SPARC inhibits breast cancer bone metastasis and may be a clinical therapeutic target.

Breast cancer is one of the most common types of cancer in females worldwide, and metastasis to bone is an important characteristic of malignancy. The present study aimed to investigate the molecular mechanism of breast cancer to bone metastasis of secreted protein acidic and rich in cysteine (SPARC). Immunohistochemistry was performed to examine the expression of SPARC in primary breast tumors and bone metastatic foci. Western blotting and reverse transcription-quantitative polymerase chain reaction were performed to detect the expression level of SPARC in several types of breast cancer cell. A Transwell filter assay was used to assess the effect of SPARC on breast cancer cell invasion ability, and an osteoblast differentiation assay was employed to analyze the effect of SPARC on the differentiation ability of mesenchymal stem cells. Clinical data revealed that decreased stromal SPARC expression is associated with breast cancer to bone metastasis. Gain- and loss-of-function studies reveal that SPARC inhibits the migration and invasion of breast cancer cells, and suppresses osteoclast activation in the breast cancer microenvironment. SPARC serves an important role in breast cancer bone metastasis and may be a promising therapeutic target for the treatment of breast cancer bone metastasis.