A real-world US study of recurrence risks using combined clinicopathological features in HR-positive, HER2-negative early breast cancer

Plain language summary Breast cancer is frequently diagnosed early, at a stage when patients can be cured. However, some patients have breast cancers (tumors) with a high risk of recurrence. When cancers come back, a cure is often not possible. This study looks at multiple high-risk tumor features and the risk of cancer returning, in the most common breast cancer type, known as hormone receptor-positive, HER2-negative breast cancer. In patients with high-risk tumors, breast cancer returned in about 11.9% of patients within 2 years and in 29.8% of patients at 5 years. The risk of recurrence or death was three-times higher in patients with high-risk tumors compared to patients with nonhigh-risk tumors. These results suggest better treatments are needed to prevent breast cancers from coming back in patients at high risk of recurrence. Aim: To assess invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in hormone receptor-positive, HER2-negative early breast cancer with combined clinicopathological criteria from monarchE, a phase III study of abemaciclib. Methods: US electronic health records were used to compare outcomes between high-risk (>= 4 lymph nodes, or 1-3 lymph nodes and grade 3, tumor >= 5 cm, or Ki-67 >= 20%) versus nonhigh-risk groups using Kaplan-Meier methods and Cox regression models. Results: The high-risk group (n = 557) was at higher risk for IDFS and DRFS events than the nonhigh-risk group (n = 3471). IDFS events (hazard ratio: 3.07; 95% CI: 2.45-3.83) and DRFS events (hazard ratio: 3.15; 95% CI: 2.49-3.97) were significantly higher for the high-risk group. Conclusion: Risk of recurrence was three-times greater in the high-risk group, highlighting the need for better therapies.