Using aromatase inhibitors in the neoadjuvant setting: evolution or revolution?

Despite improvements in the management of patients with early breast cancer, the prognosis for women with locally advanced breast cancer (LABC) remains poor. The potential goals of neoadjuvant treatment for this disease include down-sizing tumours to allow breast conservation as well as the possibility of improving survival rates. Neoadjuvant treatment was initially dominated by chemotherapy, which increased rates of breast conserving surgery, but to date has demonstrated no survival benefit over standard adjuvant chemotherapy. With recent advances in endocrine therapy, and rapid and routine assessment of predictive factors of response such as estrogen (ER), progesterone (PR) and Her2 nu receptor status, endocrine therapy has come to the forefront of research investigating a neoadjuvant alternative to chemotherapy. Early studies of neoadjuvant endocrine therapy mainly evaluated the role of tamoxifen in the treatment of elderly postmenopausal women with LABC who were unselected for ER/PR status and were unsuitable for either surgery or chemotherapy. Response rates in these patients were found to be inferior to those traditionally obtained from trials with neoadjuvant chemotherapy. Paralleling the superiority that third-generation aromatase inhibitors have shown over tamoxifen in the metastatic and adjuvant settings however, AIs have also demonstrated superiority in the neoadjuvant setting. Recent studies have shown response rates for neoadjuvant treatment with aromatase inhibitors in carefully selected hormone receptor positive patients to be comparable to those seen with neoadjuvant chemotherapy. This is particularly important as hormone receptor positive tumours have repeatedly been shown to have lower response rates to neoadjuvant chemotherapy than hormone receptor negative tumours. Neoadjuvant endocrine treatment with aromatase inhibitors has therefore evolved from being an experimental effort to palliate women with LABC unsuitable for surgery or chemotherapy, to representing a viable and possibly preferred alternative for postmenopausal women with hormone receptor positive large tumours or LABC. Further benefits of neoadjuvant trials include allowing the study of predictive biomarkers of disease in order to provide insight into therapy resistance and sensitivity, and identifying promising systemic therapies for additional testing in larger adjuvant trials.