Efficacy of Neoadjuvant Endocrine Therapy Versus Neoadjuvant Chemotherapy in ER-positive Breast Cancer: Results From a Prospective Institutional Database

Background: Although neoadjuvant chemotherapy (NACT) has been established as a standard for medically fit patients with locally advanced breast cancer, there has been renewed interest in utilizing neoadjuvant endocrine therapy (NET) for women with estrogen receptor-positive, human epidermal growth factor receptor 2-negative breast cancer. Rates of pathologic complete response (pCR) are known to be low, but data regarding down-staging and long-term outcomes are inconsistent.

Patients and methods: A prospective institutional database of patients with breast cancer treated with neoadjuvant therapy from 2012 to 2017 was analyzed to identify patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative breast cancer. Patients who received NET were compared with those who received NACT. A matched analysis (age, stage, grade) was performed to compare rates of down-staging, pCR, breast conserving surgery, and CPS+EG scores.

Results: A total of 176 patients met eligibility criteria. Of these, 111 (63%) patients received NACT, 51 (29%) received NET, and 14 (8%) received both sequentially. Women prescribed NET were older (65.5 vs. 51.2 years; P < .0001) and presented with lower clinical stage (P < .0001). The median duration of NET was 90 days. When matched, clinical down-staging was more frequent with NACT (20/51; 39%) compared with NET (11/51; 22%) (P = .032). Of these, 2% achieved pCR in each cohort. Conversion rates to breast conserving surgery eligibility were low (8% and 13% with NET and NACT; P = .70). No significant differences in CPS+EG scores were identified.

Conclusions: Significantly higher rates of down-staging were achieved with NACT compared with NET when patients were matched. This study highlights the importance of establishing tumor biology and the need for biomarkers that can be used as predictive tools to inform treatment.