Long-term outcomes of neoadjuvant endocrine therapy versus chemotherapy in luminal HER2-breast cancer

Introduction. Neoadjuvant endocrine therapy (NET) is an effective treatment modality that can downsize breast tumors in a cohort of postmenopausal women with HR-positive HER2-negative breast cancer. A lack of data regarding efficacy of NET vs neoadjuvant cytotoxic chemotherapy (NCT) leads to limited usage of NET despite its favorable toxicity profile. Perioperative endocrine therapy is mainly used for the elderly or patients with comorbidities that limit their access to NCT. The COVID-19 pandemic led to increased data of NET efficacy. Nevertheless, long-term outcomes of NET application are underrepresented in literature. Objective. Assessment of long-term outcomes in patients treated with neoadjuvant endocrine therapy (NAT) versus neoadjuvant cytotoxic chemotherapy in a cohort of postmenopausal women with HR-positive HER2-negative breast cancer. Materials and methods. We retrospectively evaluated the results of treatment of 154postmenopausal patients with luminal HER2-breast cancer who were treated with neoadjuvant systemic therapy (NET or NCT) at the State Medical Institution «St. Petersburg Clinical Scientific and Practical Center for Specialized Types of Medical Care (Oncological)» from 01.01.2019 to 31.11.2020. We analyzed data on radiological, pathomorphological and long-term treatment outcomes (rate of locoregional and overall recurrence) in two groups.Results. 154 patients received neoadjuvant hormone therapy (n=78) or neoadjuvant chemotherapy (n=76). The clinical response was evaluated according to the RECIST criteria after 12 weeks and after study treatment using MMG. Partial or complete radiological response was achieved in 41.0% (n=32) in the NET group vs 69.7% (n=53) in the NCT group (p<0.001). All patients included in the study underwent surgery. A complete pathologic response was observed in 9.2% (n=7) of patients in the chemotherapy group, and in 0% of patients in the endocrine therapy group (p=0.006). Median follow-up was 46.2 months. Progression was recorded in 23.2% (n=29) of participants, with no significant benefit of NCT over NET in the frequency of locoregional relapses (NET n=8 (10.3%) vs NCT n=4 (5.3%)) (p= 0.369) or the occurrence of distant metastases NAT n=8 (10.3%) vs NCT n=13 (17.1%)) (p=0.216). Multivariate analysis showed that only pathologic lymph node status (ypN2–3) was an independent predictor of progression (p=0.007, OR=3.2; 95%CI: 1.380-7.422). Conclusions. Long-term outcomes after neoadjuvant hormone therapy are comparable with chemotherapy in the group of postmenopausal women with luminal HER2-breast cancer. The small sample size and limited follow-up period are significant limitations of our work.