Size and Treatment Outcomes of HR+, HER2- Early Breast Cancer Population With High Risk of Recurrence: A Real-World Cohort Study With Danish Breast Cancer Cooperative Group Registry Data.

While the prognosis is generally good for hormone receptor-positive (HR+), human epidermal growth factor-negative (HER2-) early breast cancer (EBC) patients, up to 30% of patients with high-risk clinical and/or pathologic features experience recurrence. This retrospective cohort study was designed to estimate the proportion of BC patients meeting the high-risk criteria used in monarchE, a phase III study of abemaciclib, and to describe the characteristics, survival, and disease recurrence in a Danish patient population. The study cohort included all women with BC diagnosis registered in the Danish Breast Cancer Cooperative Group registry, and lumpectomy or mastectomy performed between January 1, 2010, and December 31, 2019. The patient characteristics and survival outcomes were compared between high-risk patients (≥4 positive lymph nodes or 1-3 positive nodes and grade 3 and/or primary tumor size ≥5 cm), low/moderate-risk patients, and patients with triple-negative EBC (TNBC). A total of 13.0% of the HR+, HER2- EBC patients met the high-risk criteria. Five-year invasive disease-free survival (IDFS) and distant recurrence-free survival rates (DRFS) were significantly lower in the high-risk group (73.9% and 75.9%, respectively) and the TNBC group (73.0% and 76.5%, respectively), than the low/moderate-risk group (86.1% and 87.7%, respectively) (P < .0001). This study is in line with earlier observations showing that HR+, HER2- is the most common subtype, accounting for over 70% of all BC cases. The size of the monarchE-like high-risk group aligns with previous evidence from large US cohort studies. We observed that the proportion of TNBC among all EBC patients showed a decreasing trend between 2010-2019, consistent with earlier reports. The 5-year IDFS and DRFS rates of high-risk patients observed in this study are in line with the evidence from a large US cohort study, however, slightly lower IDFS and DRFS rates at 5 years for the low/moderate-risk group were observed here. About 13.0% of the HR+, HER2- EBC patient population has a high risk of recurrence and would likely benefit from novel treatment strategies targeted for patients with a high risk of recurrence.