Abstract P2-08-02: Effectiveness of cyclin inhibitors in patients with Hispanic metastatic breast cancer: Real-world evidence from the Instituto Oncológico Nacional in Panama

Abstract Introduction: The incorporation of cyclin-dependent kinase inhibitors (CDKi) has been accompanied by significant improvements in the prognosis of advanced breast cancer with positive hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) negative status. However, Hispanic patients are frequently underrepresented in clinical trials. Consequently, this study aims to assess the efficacy of CDKi in routine clinical practice within our specific population. Methods: We conducted a retrospective analysis of patients treated with a CDKi in combination with endocrine therapy at our institution from August 2018 to December 2022. We examined demographic, clinical, therapeutic, and prognostic variables. We used the chi-square test to compare variables and estimated survival using the Kaplan-Meier method, the log-rank test, and Cox proportions for multivariable analysis. Results: 299 patients were evaluated. The median age was 62 years (range 24-90). 225 (75%) were postmenopausal, and 73 (25%) were premenopausal. ECOG performance status was as follows: 24% ECOG 0, 68% ECOG 1, 6% ECOG 2, and 2% ECOG 3. 56% of patients received hormonal therapy with or without chemotherapy as adjuvant treatment. The most common sites of metastasis were the bone, lung, and liver. 62% of patients were treated in the first line, and 38% were treated in the second line. The overall response rate was 30% in the first line and 20% in the second line. Grade 3 neutropenia was observed in 36% of patients, 5% experienced QT interval prolongation, and 32% required dose adjustment. At a median follow-up of 29.5 months, 227 patients experienced tumor progression, and 166 patients (92 in the first line and 74 in the second line) died. The median first-line progression-free survival was 22.8 months (95% CI 17.5-31.5); in the second line, it was 12.5 months (95% CI 9.3-15.6). The median overall survival in first-line patients was 49.7.4 months (95% CI 35.9-63.5), while in second-line patients, it was 31.7 months (95% CI 26.9-36.5). Independent factors associated with progression-free survival were age over 60 years (HR 0.64, 95% CI 0.48-0.85, p=0.002, use of iCDK in the second line (HR 1.72 95% CI 1.31-2.23, p= 0.001), as well as an ECOG score equal to or greater than 2 (HR 2.23, 95% CI 1.39-3.58, p=0.001) Conclusion The real-world progression-free survival and overall survival outcomes of our Latino patients using CDK4/6 inhibitors closely align with those observed in clinical trials. Citation Format: Omar Castillo-Fernandez, Jonatan Quintero, Miguel Manzano, Kayra Sanchez, Ronald Dominguez, Juan Jimenez, Mara Lim. Effectiveness of cyclin inhibitors in patients with Hispanic metastatic breast cancer: Real-world evidence from the Instituto Oncológico Nacional in Panama [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-08-02.