Background/Objectives: CDK4/6 inhibitors have changed the landscape of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (BC) management. It is essential to identify predictive and prognostic factors for the efficacy of CDK4/6 inhibitors. We aimed to investigate the differences in characteristics and outcomes of patients receiving first-line CDK4/6 inhibitors according to PgR status. Methods: This multicenter retrospective study included 351 patients treated with first-line CDK 4/6 inhibitors for HR-positive/HER2-negative metastatic BC. Patients were categorized based on their PgR expression levels, including the PgR-low (<20%) and PgR-high (≥20%) groups, and baseline characteristics, treatment responses, and survival outcomes were analyzed. Results: The median age was 57 years (range: 26–85). A total of 99 patients were premenopausal, and 252 patients were postmenopausal. There were 115 (32.8%) patients in the PgR-low group, while 236 (67.2%) were in the PgR-high group. The majority of patients (56.7%) presented with de novo metastatic disease. Visceral metastases presented in 44.2% of patients. Low PgR expression was significantly associated with lower estrogen receptor levels (p= 0.031), elevated Ki-67 levels (p= 0.002), a higher incidence of visceral metastases (p= 0.035), and recurrent disease (p= 0.019). In the multivariate analysis, low PgR expression was a significant independent predictor of worse progression-free survival (PFS) and overall survival (OS). Conclusions: We demonstrated that low PgR expression is independently and significantly correlated with shorter PFS and OS. These findings support low PgR expression as a valuable prognostic biomarker in metastatic BC patients treated with first-line CDK4/6 inhibitors.
背景/目的：CDK4/6抑制剂改变了激素受体（HR）阳性、人表皮生长因子受体2（HER2）阴性转移性乳腺癌（BC）的治疗格局。识别CDK4/6抑制剂疗效的预测和预后因素至关重要。本研究旨在探讨根据孕激素受体（PgR）状态，接受一线CDK4/6抑制剂治疗的患者在临床特征和预后方面的差异。方法：这项多中心回顾性研究纳入了351例接受一线CDK4/6抑制剂治疗的HR阳性/HER2阴性转移性BC患者。根据PgR表达水平将患者分为PgR低表达组（<20%）和PgR高表达组（≥20%），并分析其基线特征、治疗反应及生存结局。结果：患者中位年龄为57岁（范围：26-85岁）。其中99例为绝经前患者，252例为绝经后患者。PgR低表达组有115例（32.8%），PgR高表达组有236例（67.2%）。大多数患者（56.7%）为初诊转移性疾病。44.2%的患者存在内脏转移。PgR低表达与较低的雌激素受体水平（p=0.031）、较高的Ki-67水平（p=0.002）、较高的内脏转移发生率（p=0.035）以及复发疾病（p=0.019）显著相关。多变量分析显示，PgR低表达是较差无进展生存期（PFS）和总生存期（OS）的显著独立预测因子。结论：本研究证实PgR低表达与较短的PFS和OS独立且显著相关。这些发现支持PgR低表达可作为接受一线CDK4/6抑制剂治疗的转移性BC患者有价值的预后生物标志物。
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