SPARC and breast carcinoma: To clarify the function of megakaryocytes in the release of biological stimuli of the microenvironment, we assayed by immunohistochemistry the expression of SPARC, ET-1, and HGF in a xenograft model of bone metastasis (ME) (Figure 1A), prepared with human 1833 clone derived from invasive MDA-MB231 breast carcinoma cells [18].