Abstract C149: Relationship between PD-L1 expression and clinicopathological characteristics in Hispanic/ Latino women with breast cancer

Abstract Background: Programmed death ligand 1 (PD-L1) expression in breast cancer serves as a prognostic marker, particularly in aggressive subtypes like triple-negative breast cancer (TNBC), where it helps in predicting response to immune checkpoint inhibitors and guides immunotherapy use. Although several studies have assessed the prevalence of PD-L1 expression in breast cancer, data from the Hispanic population, especially in Latin American countries, is lacking. This study evaluates PD-L1 expression and its correlation with pathological features in Colombian women. Methods: Women with breast cancer tested for PD-L1 were selected from the archives of the Oncologic Pathology Department at the National Cancer Institute of Colombia from September 2021 to May 2024. Information from their pathology reports was extracted, and correlation analyses were carried out using Fisher's exact test Results: A total of 60 reports were screened, comprising 56 cases of ductal invasive breast carcinoma and 1 case of lobular invasive breast carcinoma. 48 individuals were tested using the PD-L1 22C3 antibody, with 41.67% of them being positive for PD-L1 expression. Among the 48 tumors tested with 22C3, 35 cases were classified as TNBC, and 13 cases corresponded to luminal B subtype with a low positive expression (1-10%) of estrogen receptors. The percentage of positive PD-L1 cases was 37.14% for TNBC and 53.85% for the luminal B subtype. Furthermore, 5 HER2-low cases were identified with 2 of them being positive for PD-L1 expression. In the correlation analyses, PD-L1 positive expression was significantly associated with a more aggressive histologic grade compared to PD-L1 negative tumors (p = 0.007). No significant association was found between PD-L1 expression and HR, HER2, or KI67 status, nor with age, necrosis, lymphovascular involvement, perineural invasion, desmoplastic response, or immune cell infiltration. Among the 12 individuals tested for PD-L1 with the SP142 antibody, none showed positive expression, precluding correlation analyses. Conclusion: This study highlights a significant association between PD-L1 expression and aggressive histologic grade in Colombian women with breast cancer. The findings underscore the potential of PD-L1 as a prognostic marker and its relevance in guiding immunotherapy in this population. Further research is needed to explore PD-L1 expression in broader Hispanic groups to better understand its clinical implications. Citation Format: Daniel Mendivelso-González, Patricia López- Correa, Nicolás Prada-Aceros, Alfredo E Romero-Rojas, Rafael Parra-Medina. Relationship between PD-L1 expression and clinicopathological characteristics in Hispanic/ Latino women with breast cancer [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C149.