<qa>  What is the main source of estrogen in postmenopausal women?Rationale: In postmenopausal women, the main source of estrogen is through the conversion of androgens, or sex hormones produced by the adrenal glands. An enzyme called aromatase carries out this process. Exemestane, an aromatase inhibitor, blocks production of estrogens. Research indicates that the gene responsible for aromatase activity is CYPO19. Therefore, exemestane helps to inhibit aromatase activity through CYP019. Along with CYP019, another gene associated with breast cancer is an overexpression of COX-2 enzymes. Research suggests that COX-2 overexpression can cause cancer cell division, increased blood flow to tumors, and metastases. Celecoxib blocks COX-2 activity and produces fewer side effects compared with other non-steroidal inflammatory drugs NSAIDs. This study builds on previous research to test the combination of exemestane and celecoxib for breast cancer. 