The Clinical Impact of Neoadjuvant Endocrine Treatment On Luminal-Like Breast Cancers and Its Prognostic Significance: Results From a Single-institution Prospective Cohort Study

Abstract

Purpose: Neoadjuvant endocrine treatment (NET) has become a useful tool for the downstaging of luminal-like breast cancers in postmenopausal patients. It enables us to increase breast conserving surgery (BCS) rates, and provides an opportunity for assessing in vivo NET effectiveness and studying any biological changes that may act as valid biomarkers. The purpose of this study was to evaluate the safety and effectiveness of NET, and to assess the role of Ki67 proliferation rate changes as an indicator of endocrine responsiveness.Methods: From 2016 to 2020, a single-institution cohort of patients treated with NET and further surgery was evaluated. In patients with Ki67≥10%, a second core biopsy was performed after four weeks. Information regarding histopathological and clinical changes was gathered.Results: A total of 115 estrogen receptor positive (ER+)/HER2 negative patients were included. The median treatment duration was 5.0 months (IQR: 2.0-6.0). Median maximum size in the surgical sample was 40% smaller than pretreatment size measured by ultrasound (p<.0001). Median pretreatment Ki67 expression was 20.0% (IQR: 12.0-30.0), and was reduced to 5.0% (IQR: 1.8-10.0) after four weeks, and to 2.0% (IQR: 1.0-8.0) in the surgical sample (p<.0001). BCS was performed on 98 patients (85.2%). No pathological complete responses were recorded. A larger Ki67 fold-change after four weeks was significantly related to a PEPI score of 0 (p<.002). No differences were observed between luminal A- and B-like tumors with regard to fold-change and PEPI score.Conclusions: In our cohort, NET has proven effective for tumor size and Ki67 downstaging. This results in a higher rate of conservative surgery, aids in therapeutic decision-making, provides prognostic information, and constitutes a safe and well-tolerated approach