PTGS2 and breast cancer: The Transwell assay demonstrated that the number of MCF-7 breast cancer cells penetrating through the plasma membrane in the COX-2-shRNA group was 235.5±25.6 at 24 h post-transfection, which was significantly lower than that of the blank (587.3±35.2) and mock (580.5±40.7) groups (P<0.05) (Fig. 4A).