PTGS2 and breast cancer: Contrary to several studies relating COX-2 expression to parameters that characterized the aggressiveness of breast cancer, such as large tumor size, axillary lymph node metastasis, high histologic grading, negative hormone receptor status and positive Her-2 status, [9, 11, 10, 30, 8] our results indicate that COX-2 protein expression has a positive correlation with ER.