Abstract P2-10-12: Pembrolizumab in Early Triple-negative breast cancer: Real world data in Hispano-American women (PETRHA) - Initial results

Abstract Currently, the standard of care for women with stage II-III triple-negative breast cancer (TNBC) includes neoadjuvant chemotherapy combined with pembrolizumab, followed by adjuvant pembrolizumab. Notably, approximately 10% of the participants in the KEYNOTE-522 trial were Hispanic or Latino, highlighting a gap in evidence regarding the benefit of pembrolizumab in this population. This study aims to evaluate the efficacy and safety of pembrolizumab in patients diagnosed with early TNBC treated in the region. Hispano-American women diagnosed with early TNBC, including estrogen and progesterone receptors <10%, who received pembrolizumab as part of their systemic therapy were included in this multicenter retrospective cohort. Descriptive statistics were used to analyze sociodemographic and clinicopathological characteristics. Independent samples T-test, X2, and Fisher’s exact tests were used to evaluate associations between variables, employing logistic regressions to calculate odds ratios (OR) when appropriate. A total of 214 patients were included. 116 (54.2%) lived in Mexico, 53 (24.8%) in Argentina, 19 in Chile (8.9%), 18 in Colombia (8.4%), and 8 (3.7%) in Peru. Most women (58.2%) received cancer care in the private setting and the remaining in public/governmental settings. The median age at diagnosis was 44.0 years (IQR: 36.0 - 53.0 years), 57.7% were premenopausal, and 63.6% had node-positive disease. Neoadjuvant pembrolizumab was administered 200 mg q3w in 83.7% and 400 mg q6w in 16.3% of patients. Seventy-three (34.1%) patients did not complete the planned number of neoadjuvant pembrolizumab cycles (8 cycles for q3w and 4 cycles for q6w). The reasons for not completing neoadjuvant pembrolizumab were immune-related adverse events (irAEs) (29/73; 39.7%), lack of access (26/73; 35.6%), disease progression (6/73; 8.2%), patient decision (1/73; 1.4%), and other (24/73; 32.9%). Patients treated in the private sector were more likely to complete neoadjuvant pembrolizumab than those in public or government-funded settings (66.7% vs 33.3%, p = 0.002). The rate of pathological complete response (pCR) was 59.9% in the overall population, with a higher pCR rate among patients who completed the planned number of pembrolizumab cycles compared to those who received an incomplete number of cycles (69.8% vs. 42.5%, p<0.01, respectively). When considering patients who did not complete the standard number of neoadjuvant chemotherapy cycles, only an incomplete number of pembrolizumab cycles emerged as a predictive factor for non-PCR, with an OR of 0.32. irAEs occurred in 32.5% and 44.4% of those who completed and did not complete the planned number of pembrolizumab cycles, respectively. Overall, the most frequent any-grade irAEs were hypothyroidism (14.1%), rash (9.6%), and hepatitis (9.1%). No grade 5 irAEs were reported. The efficacy and safety of neoadjuvant pembrolizumab in our population is consistent with data from the pivotal trial. However, our study highlights several key aspects regarding the treatment of early TNBC in Hispano-American women using neoadjuvant pembrolizumab. Disparities in access to pembrolizumab therapy were reflected as women with private insurance were more likely to complete pembrolizumab compared to those in public or governmental settings. Additionally, our study found a significantly lower pCR rate among women who did not complete the planned number of pembrolizumab cycles, underscoring the importance of treatment adherence. These findings emphasize the need for strategies to improve access to pembrolizumab, manage irAEs in a timely and appropriate manner, and support patients in completing their treatment regimens in our region. This work was conducted on behalf of the Latin American Breast Cancer Association (LABCA). Citation Format: Daniela Vazquez-Juarez, Alejandro Aranda-Gutierrez, Yanin Chavarri-Guerra, Fernando E. Petracci, Omar Peña-Curiel, Ernesto Korbenfeld, Felix Urtasun, Francisco Acevedo, Enrique Jose Zamudio Lozoya, Luisa Fernanda Gonzalez Gonzalez, William Armando Mantilla, Sandra Franco, Claudia Haydee Arce Salinas, Karla Alicia Centelles López, Eva Willars, Monserrat Alvarado Hernandez, Bertha Alejandra Martinez-Cannon, Henry Gomez, Maricela Garcia Garces, Angel Lopez-Galindo, Mauricio Lema, Camila Lema, Cynthia Villarreal-Garza. Pembrolizumab in Early Triple-negative breast cancer: Real world data in Hispano-American women (PETRHA) - Initial results [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 P2-10-12.