Prognostic significance of ER-to-PR difference in ER+/HER2- early breast cancer

ER+/HER2- breast cancer is a common subtype of breast cancer. This study aimed to evaluate the prognostic value of ER-to-PR difference (EPD) in ER+/HER2- early breast cancer (EBC). A retrospective cohort study was conducted, including 3,340 ER+/HER2- EBC patients, divided into a training cohort of 2,873 patients and a validation cohort of 467 patients. The optimal EPD cutoff value for stratifying patients was determined using X-tile. Additionally, the prognostic value of EPD, when combined with other clinicopathological factors, was assessed using the Cox proportional hazards model and five traditional machine learning methods. The optimal cutoff value for EPD was determined as 10%, categorizing patients into EPD-low (ER-PR ≤ 10%) and EPD-high (ER-PR > 10%) expression groups. Patients with EPD-high tumors exhibited a poorer prognosis compared to those with EPD-low tumors. In the multivariate Cox model, EPD was identified as an independent prognostic factor for disease-free survival (DFS) (HR: 1.496, P = 0.004). Integrating EPD with clinicopathological parameters into a predictive model effectively predicts DFS in ER+/HER2- EBC patients. In the most effective CoxPH model, the area under the curve (AUC) values for predicting 3-year, 5-year, and 7-year DFS were 0.718, 0.702, and 0.701, respectively, in the WCH cohort, and 0.770, 0.739, and 0.743, respectively, in the FUSCC cohort. EPD may serve as a novel prognostic marker, allowing for the identification of a population with a poor prognosis in ER+/HER2- EBC, thereby aiding clinical decision-making.