A narrative review: research progress of adjuvant intensive endocrine therapy for early breast cancer

Hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR⁺/HER2^-) breast cancer (BC) is the most prevalent subtype of all BCs. The primary treatment modality is endocrine therapy (ET). Traditional adjuvant ET for early-stage breast cancer (EBC) has undergone extensive exploration and is relatively well-established. However, patients at high risk of recurrence may still experience early relapse, necessitating consideration of intensified adjuvant ET to reduce recurrence risk. The objective of this narrative review is to examine various strategies for intensifying adjuvant ET in EBC, thoroughly analyze key clinical studies, and summarize the most effective treatment approaches supported by current evidence-based medicine. Furthermore, it addresses unresolved challenges that necessitate further refinement and investigation.

As of March 2024, a comprehensive literature search, compilation, and analysis were conducted across PubMed, Baidu Scholar, ClinicalTrials.gov, and relevant academic conferences.

There are numerous methods to intensify adjuvant ET: (I) combining ovarian function suppression (OFS) to reduce estrogen levels in the body and induce a state of artificial menopause to enhance the efficacy of ET; (II) individual extension of the duration of ET based on patients' varying risks of recurrence, with high-risk patients covering two peak recurrence periods; (III) the addition of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) can significantly extend invasive disease-free survival and reduce the risk of recurrence, serving as the main intensive treatment for high-risk patients; (IV) combination with bone-modifying drugs (BMD) can significantly reduce rates of bone metastasis and slightly enhance prognosis but is not commonly used in adjuvant settings; (V) combined with poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors, current studies only show a trend towards benefit in HR⁺ patients with germline BRCA1/2 mutations; more data are still needed to support its clinical benefit. This narrative review examines various strategies for intensifying adjuvant ET in EBC, critically evaluates key clinical studies, and summarizes the most effective treatment approaches supported by current evidence-based medicine. Furthermore, it addresses unresolved challenges that necessitate further refinement and investigation.

In the context where traditional adjuvant ET is relatively well-established, the emergence of novel ET has notably addressed issues of endocrine resistance more effectively. Various intensified adjuvant ET has shown potential in further reducing recurrence risk among high-risk patients. However, additional research and time are essential to determine the optimal approaches for intensified adjuvant ET.