Skipping Hormone Therapy in Low-Risk Early Breast Cancer

Breast cancer is the most frequently diagnosed cancer among women worldwide. Hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) tumors represent the predominant subtype and are generally associated with favorable outcomes. Adjuvant endocrine therapy (ET), including tamoxifen and aromatase inhibitors, constitutes a cornerstone of treatment for HR+/HER2- early breast cancer and has demonstrated reductions in recurrence and mortality in large randomized trials and meta-analyses. However, these benefits were mainly established in populations including patients with a broader spectrum of recurrence risk.

The implementation of mammography screening programs has increased the detection of small, early-stage breast cancers, including tumors with excellent prognosis and very low risk of recurrence. In postmenopausal women with small node-negative Luminal A tumors, recurrence rates are particularly low, raising concerns regarding potential overtreatment and the balance between treatment benefit and toxicity.

Although ET is effective, its long-term administration is associated with substantial treatment burden and persistent toxicities, including musculoskeletal symptoms, vasomotor symptoms, fatigue, sexual dysfunction, mood disturbances, and bone loss. These adverse effects may significantly affect quality of life and contribute to treatment discontinuation. Observational data have suggested that ET-related quality-of-life impairment may persist longer than chemotherapy-related effects, particularly in postmenopausal women.

Retrospective studies have suggested that the absolute benefit of ET may be limited in selected patients with very low-risk disease, especially among older women with small, low-grade HR+/HER2- tumors. Furthermore, simulation models estimating individualized treatment benefit indicate that the absolute overall survival gain associated with ET in some low-risk subgroups may be minimal, with high numbers needed to treat.

Advances in biological characterization have enabled identification of Luminal A tumors, characterized by strong hormone receptor expression, low proliferative activity, and favorable prognosis. Combining biological characteristics with clinicopathological features such as age, tumor size, grade, and nodal status allows the identification of a subgroup of postmenopausal patients with exceptionally low risk of relapse.

NoELA was developed to prospectively evaluate a therapeutic de-escalation strategy consisting of omission of adjuvant ET in postmenopausal women presenting with very low-risk HR+/HER2- early breast cancer with Luminal A phenotype. The study focuses on patients expected to derive limited benefit from ET while remaining exposed to its long-term toxicity burden.

The study also aims to generate evidence supporting more individualized treatment strategies and improved shared decision-making by better quantifying the risk-benefit balance of ET omission in this population. In addition, comparison with external real-world data derived from patients treated with standard ET will help contextualize outcomes and improve the external validity of the findings.