Oral exemestane 25 mg/day for 2–3 years of adjuvant therapy was generally more effective than 5 years of continuous adjuvant tamoxifen in the treatment of postmenopausal women with early-stage estrogen receptor-positive/unknown receptor status breast in a large well-designed [ citation needed ] trial. Preliminary data from the open-label TEAM trial comparing exemestane with tamoxifen indicated in 2009 that exemestane 25 mg/day is also effective in the primary adjuvant treatment of early-stage breast cancer in postmenopausal women. 
Drugs like exemestane and other steroidal aromatase inhibitors have a steroidal structure that competes with the natural aromatase substrate androstenedione .  The inhibitor must share important structural features with the endogenous substrate, and as features of the androgens , allowing them to interact with the catalytic site on the enzyme protein. This renders the steroidal aromatase inhibitors inherently selective.  Due to its selective inhibition it will not affect the production of the other steroids in the estrogen biosynthetic pathway.