Efficacy and Safety of Dalpiciclib in HR-Positive Advanced Breast Cancer: A Two-Center Retrospective Study

<b>Background</b>: This study aims to evaluate the real-world efficacy and safety of dalpiciclib in patients with hormone receptor-positive (HR+) advanced breast cancer and explore the impact of different clinical characteristics on treatment outcomes. <b>Methods</b>: This was a two-center, retrospective cohort study involving 76 patients treated with dalpiciclib between January 2022 and June 2024 at two affiliated hospitals of Anhui Medical University in China. Data on progression-free survival (PFS), adverse events, and key clinical factors were collected and analyzed. Kaplan-Meier estimates were used for statistical analysis. <b>Results</b>: The median PFS (mPFS) for the entire cohort was 12.00 months (95% CI: 10.09-13.91 months). Patients receiving dalpiciclib as first-line therapy had significantly better outcomes (mPFS: 17.00 months, 95% CI: 9.19-24.81 months) than those receiving later-line therapy (<i>p</i> < 0.001). Patients with prior exposure to cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) and those with endocrine resistance had poorer outcomes. Multivariate Cox proportional hazards regression analysis confirmed that earlier treatment line (HR for second-line vs. first-line: 3.89, <i>p</i> = 0.015; HR for third-line or later vs. first-line: 5.56, <i>p</i> = 0.006) and prior CDK4/6i treatment (HR = 3.42, <i>p</i> = 0.040) were independent predictors of PFS. The most common adverse events were hematologic toxicities, including leukopenia (76.6%) and neutropenia (72.4%), mostly grade 1-2. No febrile neutropenia cases were reported, indicating a manageable safety profile. <b>Conclusions</b>: Dalpiciclib combined with endocrine therapy is associated with favorable efficacy and safety in real-world settings, with early-line treatment and lower tumor proliferative activity associated with better outcomes. While findings suggest potential for clinical application, further large-scale prospective studies are needed to validate its effectiveness in different patient subgroups and optimize treatment strategies.