Abstract P1-12-07: Neo-Adjuvant Exemestane in Post Menopausal Estrogen and/or Progesterone Receptor Positive Breast Cancer: A Randomized Phase II Trial To Investigate Optimal Duration (4 Month Versus 6 Month) of Preoperative Endocrine Therapy (PTEX46 Trial)

Background: Since the 1990s, primary endocrine therapy has been considered the gold standard in the adjuvant and metastatic treatment settings for estrogen and/or progesterone receptor (ER and/or PgR) positive breast cancer. This therapy has also been shown to be effective as neo-adjuvant endocrine therapy in these indications. In recent years, the focus of clinical interest has shifted to the third-generation aromatase inhibitors from tamoxifen. The optimal treatment duration time and causal relationship between neo-adjuvant endocrine therapy and survival, however, are not clear. We therefore conducted the present study to investigate the potential benefits of neo-adjuvant exemestane (E) therapy with the goal of identifying the optimal treatment duration (4 months versus 6 months). Methods: Conducted at three hospitals in Japan, this study was a multicenter, randomized phase II trial of pre-operative E treatment in postmenopausal women with untreated primary breast cancer. Fifty postmenopausal women with ER positive and/or PgR positive invasive breast cancer were randomly assigned to E (25 mg/day) for 4 months (4 mo) or E (25 mg/day) for 6 months (6 mo). All patient data were collected by UMIN and were analyzed by the National Cancer Center in Japan. Tumor regression (by clinical examination, ultrasound, and MRI), pathological response, shift towards breast-conserving surgery, and safety assessments were the main outcome measures. Results: Of the 50 patients that enrolled, 28 patients had undergone surgery. The mean ages in the 4 mo and 6 mo treatment groups were 66.7 years and 66.8 years, respectively. No significant differences in the patient characteristics were found in the two groups. The response rates (partial or complete responses) by clinical examination in the 4 mo and 6 mo groups were 37.5% and 50%, respectively. Pathological responses (minimal response or better) were found in 13.3% and 41.7% of patients and a partial mastectomy was performed in 50.0% and 58.3% of patients after 4 mo and 6 mo, respectively. Conclusion: To date, the results of this study demonstrate that treatment with E for 6 mo was more efficacious than treatment with E for 4 mo. Further work is in progress to obtain data from additional patients and to identify the optimal duration of neo-adjuvant E. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-12-07.