Optimal Treatment Duration of Neoadjuvant Endocrine Therapy for Women Aged 60 Years or Older with Estrogen Receptor-Positive, HER2-Negative Invasive Breast Cancer

Background: Neoadjuvant endocrine therapy is not the standard of care for breast cancer, primarily because the optimal treatment duration remains unclear. This phase 2 prospective multicenter study analyzed time to progression, time to maximal response, and time to treatment failure for neoadjuvant exemestane. Methods: Inclusion criteria were women aged ≥60 years with Stage II or III breast cancer classified as estrogen receptor-positive/human epidermal growth factor receptor 2-negative. Response was defined as a ≥10% and minimum of 3 mm decrease in tumor size, as compared with the most recent or smallest value, and no new lesion. Progression was defined as a >10% and minimum of over 3 mm increase in tumor size, as compared with the most recent or smallest value, or a new lesion. Maximal response was defined as the final recorded response. Results: This study included 24 women, most of whom had T2 N0 tumors with high estrogen receptor expression. We initially observed a response in 23 patients (96%); however, 6 patients (25%) later experienced progression. Time to progression, time to maximal response, and time to treatment failure ranged from 7 to 22 months (estimated median, 35), 1 to 22 months (estimated median, 10), and 2 to 22 months (estimated median, 22), respectively. Treatment duration varied widely, but the estimated optimal duration of neoadjuvant exemestane therapy was 22 to 35 months in patients seeking to avoid surgery and 10 months in patients wishing to receive breast-conserving surgery. Conclusions: Neoadjuvant exemestane therapy is long effective for older women with hormone-sensitive breast cancer.