Current role and safety profile of aromatase inhibitors in early breast cancer

The current adjuvant therapy for breast cancer is in a continous progress; standard therapeutic strategies include the use of chemotherapy, molecular targeted drugs and hormonal agents, according to well-established prognostic and predictive factors. Among the hormonal drugs, for a long period tamoxifen has been the gold standard of adjuvant therapy in postmenopausal women with hormone receptor-positive (HR+) early breast cancer. In the last years an expanding use of aromatase inhibitors occurred in this subset of patients, because the third-generation class of these agents (anastrozole, letrozole and exemestane) showed to be more effective and safe than tamoxifen and are now recommended as the preferred hormonal approach to postmenopausal hormone-sensitive patients, according to national and international guidelines. Treatment choices with these agents include the use of an aromatase inhibitor as an upfront strategy for 5 years, as a sequential approach after 2-3 years of tamoxifen, or as an extended use after the classical 5 years of tamoxifen. The improved efficacy of aromatase inhibitors over tamoxifen has been largely demonstrated in terms of better disease-free survival, reductions in the occurrence of early distant metastasis as well as improvement of overall survival. Moreover, according to the optimal duration of therapy, presently it is not known whether aromatase inhibitor therapy, as tamoxifen, should be limited to 5 years. In terms of safety profile, the side effects of aromatase inhibitors, as compared with selective estrogen receptor modulators, are different, reflecting the specific mechanism of action of these drugs. There is strong evidence that aromatase inhibitors are well tolerated, with a lower incidence of gynecological symptoms (vaginal bleeding, discharge and endometrial neoplasia), venous thromboembolic events and hot flushes than tamoxifen. On the other hand, the use of aromatase inhibitors has been associated with loss of bone density, arthralgia, myalgia, and a negative effect on lipid metabolism and cardiovascular risk. More extensive and mature studies are necessary to well establish the safety of aromatase inhibitors when given to patients with breast cancer for a long time.