Exemestane as primary systemic treatment for hormone receptor positive post-menopausal breast cancer patients: a phase II trial of the Austrian Breast and Colorectal Cancer Study Group (ABCSG-17)

Background A multicenter phase II study was conducted to analyze the clinical activity of the steroidal aromatase inhibitor exemestane in the neoadjuvant treatment of post-menopausal women with strongly ER- and/or PgR- positive operable breast cancer. Patients and methods From September 2000 to December 2003, 80 women were recruited for treatment with exemestane 25 mg once daily for 4 months. The primary end-point was the clinical response rate according the WHO criteria; the secondary end-points included toxicity and the number of patients who qualified for breast conserving surgery at the end of treatment, comparability of evaluation methods for response, potential alterations of hormone receptor and Her2/neu status during treatment. Results On an intention to evaluate analysis, according to the prespecified criteria the overall clinical objective response rate was 34%, the pCR rate was 3% and the rate of breast conserving surgery was 76%. When sonographic and mammographic longitudinal measurements were included in patients with missing palpation data, response rates were 38% and 41%, respectively. The tumor response was independent of the Her2/neu status which remained unchanged during treatment. In contrast, while the ER expression remained unaltered, downregulation of the PgR was observed. The treatment was well tolerated with no grade 3 and 4 toxicities except gastrointestinal (one grade 3 case) and hot flushes (two grade 3 cases). Conclusion This study shows that exemestane is effective and safe as a preoperative therapy in post-menopausal patients with strongly hormone receptor-positive breast cancer.