PTGS2 and breast cancer: MDA-MB-231 cells silenced for COX-2 expression showed reduced mRNA expression of several oncogenic markers, including IL-11, a marker for metastasis of breast cancer to bone, the Notch1 receptor ligand JAG1, whose expression is correlated with poor breast cancer prognosis, CXCR4, a receptor involved in cancer cell invasion, and matrix metalloproteinase-1 (MMP-1), a secreted enzyme responsible for the degradation of the stroma during breast cancer cell invasion.