PTGS2 and breast cancer: In all, 23 studies were excluded as the samples were taken adjacent to breast cancer or from patients who previously had breast cancer (n=11), the proportion (%) of COX-2 expression was not reported or could not be calculated (n=9), the study did not use monoclonal anti-COX-2 antibodies (n=2) or did not report independent evaluation of COX-2 staining by two assessors (n=1).