Progesterone receptor expression and survival outcomes in metastatic breast cancer: A retrospective analysis of CDK4/6 inhibitor–treated patients in a tertiary care center.

e13069 Background: Progesterone receptor (PR) status significantly impacts breast cancer prognosis, yet its role in Mexican metastatic breast cancer (MBC) patients remains poorly explored. This study evaluates PR expression and survival outcomes in MBC patients treated with CDK4/6 inhibitors at a tertiary care center. Methods: This retrospective study included MBC (Stage IV o recurrent) patients with documented hormone receptor (HR) and PR status. Clinical features, treatment data, and metastatic sites were analyzed. We used Spearman's correlation for PR and treatment duration, Kruskal-Wallis test for PR distribution across metastatic sites, and Kaplan-Meier survival analyses for progression-free survival (PFS) and overall survival (OS). Mann-Whitney U test was used to assess non-parametric data. A p-value < 0.05 was considered significant, with Bonferroni correction applied. Results: Among 129 patients (median age: 64 years), 23.26% were premenopausal. Clinical stages were: II (33.33%), III (37.98%), IV (24.03%). Luminal A subtype was present in 53.49%. Median adjuvant hormone therapy duration was 33.5 months. Overall survival (OS) was measured from the time of recurrence until the occurrence of an event (death), and progression-free survival (PFS) was measured from the initiation of CDK4/6 inhibitor therapy until treatment failure (disease progression). Mean OS was 54.81months, and mean PFS was 18.22 months. Patients with PR < 10% (n = 31) had a mean PFS of 15.71 months and OS of 41.47 months. Those with PR > 10% (n = 98) had a mean PFS of 19.77 months and OS of 59.12 months, with no significant differences (p > 0.05). A weak negative correlation was observed between PR and hormonotherapy duration (Spearman’s ρ = -0.188, p = 0.033). Conclusions: This study outlines the impact of PR positivity on survival in MBC. While PR < 10% and > 10% showed numerical differences in OS and PFS, these were not significant. Further research is needed to explore PR's clinical relevance in MBC management. Characteristic Value Patients 129 Median Age 64 years (32–90) Age Distribution >55: 97 (75.19%); <55: 31 (24.03%) Menopausal Status Premenopausal: 30 (23.26%); Postmenopausal: 99 (76.74%) Clinical Stage II: 43 (33.33%); III: 49 (37.98%); IV: 31 (24.03%) Subtype Luminal A: 69 (53.49%) Adjuvant Hormone Therapy Duration Median: 33.5 months (1–120) CDK4/6 Inhibitors Palbociclib: 71 (55.04%); Ribociclib: 42 (32.56%); Abemaciclib: 14 (10.85%) Survival Outcomes Mean PFS 18.22 months (1.5 years) Mean OS 54.81 months (4.5 years) PFS by PR Positivity <10%: 15.71 months; >10%: 19.77 months (p > 0.05) OS by PR Positivity <10%: 41.47 months; >10%: 59.12 months (p > 0.05) *PFS by PR Positivity: PR <10% had numerically lower mean PFS (15.71 months) vs. PR >10% (19.77 months); difference not statistically significant (p > 0.05). **OS by PR Positivity: PR <10% had numerically higher mean OS (41.47 months) vs. PR >10% (59.12 months); difference not statistically significant (p > 0.05).