A prospective cohort study of clinical characteristics and outcome of Chinese patients with estrogen receptor-negative/progesterone receptor-positive early breast cancer

Abstract Background There has been a debate about whether the estrogen receptor (ER) -negative/progesterone receptor (PR) -positive breast cancer exists or is an artefact. Further, there have been conflicting results as to whether PR is a molecular marker for the benefit of adjuvant endocrine therapy (ET). Methods Early breast cancer patients of West China Hospital were divided into the ER-/PR+ group, ER+ group and ER-/PR- group. The Chi-square test was employed to analyze the differences in clinical and pathological features among the three groups. Multivariate Cox regression and Kaplan-Meier survival analysis were employed to compare the survival difference between all patients of the three groups, between the patients who had received ET of the three groups, and between patients who had or had not received ET in the ER-/PR+ group. Finally, we analyzed which subgroups of ER-/PR+ patients would benefit from ET. Results From 2008 to 2020, we enrolled 10494 early breast cancer patients with definite ER and PR status. 445, 7129, and 2920 patients were in the ER-/PR+ group, ER+ group and ER-/PR- group, respectively. ER-/PR+ group displayed unfavourable clinical and aggressive pathological characteristics than the ER+ group. The breast cancer-specific survival (BCSS), local recurrence-free survival (LRFS) and distant disease-free survival (DDFS) of the ER-/PR+ group were worse than those of the ER+ group. After ET, the ER-/PR+ group still had a worse BCSS, LRFS and DDFS than those in the ER+ group. Patients who received ET in the ER-/PR+ group showed significantly better LRFS and BCSS than patients who did not, but there was no difference in DDFS. Subgroup analysis suggested ER-/PR+ patients with PR≥10% instead of PR<10% could benefit from ET. Conclusion The ER-/PR+ group has unfavourable clinic-pathological features and a worse prognosis than the ER+ group. ET still reduces endpoint events of LRFS and BCSS but could not reduce DDFS endpoint events. Further, subgroup analysis suggests ER-/PR+ patients could benefit from ET when PR expression is≥10%.