Abstract PO3-09-04: Identification of germline pathogenic variants to guide systemic therapy: Prevalence and spectrum of PVs among Mexican patients with metastatic breast cancer

Abstract BACKGROUND Currently, international genetic cancer risk assessment (GCRA) guidelines recommend genetic testing for the identification of germline pathogenic variants (PVs) in patients with metastatic breast cancer (MBC) to guide systemic therapy. Patients with PVs in BRCA genes are candidates to receive poly(adenosine diphosphate–ribose) polymerase inhibitors (PARPi). The prevalence of PVs in patients with HER2-negative MBC has been reported to be 10%. The proportion of MBC in low- and middle-income countries (LMIC) is higher. However, access to genetic testing in LMIC is limited and contributes to the gap in genetic epidemiology knowledge. We aimed to describe the frequency of germline PVs in breast cancer associated genes and clinic-pathologic characteristics of Mexican women with MBC. METHODS This retrospective study included Mexican women from 7 centers in Mexico, who were diagnosed with MBC and had genetic testing. Pathogenic and likely pathogenic variants were reported. Demographic, histopathological characteristics, family history and access to treatment with PARPi, were obtained from chart review. RESULTS From August 2017 to May 2023, 114 Mexican women with MBC were included, median age at diagnosis was 47 years (range 24-80 y), 42% had de novo metastatic, and 58% recurrent disease. 86.8% had infiltrating ductal carcinoma, 51.3% had HR+HER2- (n=58), 4.4% HR+HER+ (n=5), 5.3% HR-HER2+ (n=6), and 38.6% triple negative tumors (n=44). Sites of metastatic disease were as follows: 61.4% non-regional nodes (n=70), 57% bone (n=65), 40.3% lung (n=46), 30.7% liver (n=35), 15.8% central nervous system (n=18) and 7% peritoneal carcinomatosis (n=8). The frequency of PVs was 22% (25/114); 84% of the PVs were heterozygous, mainly identified in BRCA genes (BRCA1 n=12, BRCA2 n=9), and in 4 patients in other genes (PALB2 n=2, PTEN n=1, MUTYH n=1). Among PARPi candidates, 40% (10/25) received Olaparib, the majority received it on the second or subsequent lines of treatment (7/10) with a median progression free survival of 6 months (3-13 m). BRCA carriers were younger at BC diagnosis (38.5 vs. 49 years, p=0.00694) and had a significant higher proportion of family history of ovarian cancer (p=0.00039), but not for breast (p=0.06), prostate (p=0.71) or pancreatic cancer (p=0.098), compared to non-carriers. CONCLUSION We found a high frequency of PVs in BRCA genes in Mexican women with MBC. Access to the genetic testing and targeted therapy should be improve in the Mexican population in order to decrease disparities in cancer care in the Mexican Population. In addition, genetic testing allows to identify other family members at risk with cascade testing and to recommend them risk reduction strategies. Citation Format: Jose Luis Rodriguez-Olivares, Maria Fernanda Esparza-Orozco, Jose Alfredo Ramirez-Gonzalez, Roberto Ivan Sanchez-Reyes, Enrique Isay Talamantes-Gamez, Gregorio Quintero-Beulo, Gilberto Lopez-Rosas, Karla Alicia Centelles-López, Brizio Moreno-Jaime, Daniela Vazquez-Juarez, Ana Maria Hernandez-Murillo, Ilana de la Puente Tawil, Jeffrey Weitzel, Cynthia Villareal Garza, Yanin Chavarri-Guerra. Identification of germline pathogenic variants to guide systemic therapy: Prevalence and spectrum of PVs among Mexican patients with metastatic breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-09-04.