Accordingly, in vitro studies have shown that mechanical stimulation of osteocytes reduces the transendothelial migration of breast cancer cells and that the osteocyte–endothelial cell interaction inhibits the expression of matrix metalloproteinase 9 (MMP-9), an enzyme involved in the invasion of metastatic cancer cells through the extracellular matrix [46]. The gene discussed is MMP9; the disease is metastatic malignant neoplasm.