Abstract PS3-03-22: Brca1/2-tested breast and ovarian cancer patients in peru: clinical and genomic features

Abstract Pathogenic and likely pathogenic (P/LP) variants in BRCA1/2 are key markers of hereditary cancer, guiding clinical and preventive care. In Peru, late-stage diagnoses and limited genetic services make breast and ovarian cancer major public health issues. This study aimed to describe the clinical and genomic characteristics of Peruvian patients with breast and/or ovarian cancer who underwent BRCA1/2 testing between 2013 and 2020. Ten-year overall survival was analyzed using univariate and multivariate Cox regression, with left truncation to minimize immortal time bias. METHODS This study includes individuals diagnosed with breast and/or ovarian cancer referred to a Medical Genetics evaluation at the Instituto Nacional de Enfermedades Neoplásicas (INEN) during the period of August 2013 to March 2020. Individuals who met clinical criteria to be included in the inter-institutional protocol INEN13-48: “Estudio del Cáncer Hereditario y Familiar en Población Peruana” as part of the “Molecular Genetic Studies in Cancer patients and their relatives”; IRB #96144 City of Hope (COH); accessed genetic testing (carried out at COH). In patients diagnosed with both breast and ovarian cancer, only the first diagnosed cancer was considered for classification. RESULTS A total of 1,576 patients were included in the study, with a median age at diagnosis of 41 years. The vast majority were female (99.3%), and only 0.7% (n = 11) were male. Family history of cancer was absent in 61% of cases; 18% reported first-degree relatives with breast and/or ovarian cancer, while 20% reported other types of cancer. Breast cancer was diagnosed in 89.5% of patients (n = 1,410), ovarian cancer in 8.5% (n = 134), and both in 2% (n = 32). In breast cancer cases, the most frequent tumor subtype was HR+/HER2− (39.6%), followed by triple-negative (31.3%) and HER2+ (28.1%). Overall, we identified pathogenic variants in BRCA1 were identified in 7.2% (n = 114) of the whole population, and in BRCA2 in 3.2% (n = 51). Specifically, 6% of breast cancer patients carried a BRCA1 pathogenic variant, and 3% had a BRCA2 variant. BRCA1-positive breast tumors were predominantly of the triple-negative subtype (85.4%), whereas HR+/HER2- (47.6%) tumors were the most frequent among BRCA2-positive cases. In patients with ovarian cancer, 82% were BRCA-negative, while 14% carried BRCA1 and 2.8% BRCA2 pathogenic variants. Clinical stage II was the most common at presentation (39.3%), followed by stage III (38.8%), stage I (11%), and stage IV (10%). Additionally, 15% of patients developed a second primary malignancy, most commonly a new breast cancer (52%), followed by other cancers (15%), thyroid (12%), ovarian (8%), and colorectal cancer (6%). Notably, ovarian cancer diagnosis, advanced clinical stage, and triple-negative breast cancer subtype were significantly associated with poorer overall survival (p 0.001 for all). CONCLUSIONS Patients carrying pathogenic BRCA variants were found to have a higher risk of developing a second primary cancer, mainly a new breast cancer, reinforcing the need for long-term surveillance in this population. In the subgroup of breast cancer patients with BRCA1 mutations, a higher incidence of triple-negative tumors was observed, whereas BRCA2-mutated patients more commonly exhibited luminal subtypes. These findings underscore the importance of strengthening genetic counseling services and implementing risk-reduction strategies as well as precision oncology programs. Given the higher mortality observed in patients with BRCA1 mutations, it is essential to understand the clinical and genomic profiles of these individuals to optimize cancer care for high-risk populations in the country. Citation Format: P. Mora, N. Valdiviezo, M. Acosta, J. Herzog, L. Reynaga, L. Taxa, T. Vidaurre, Y. Sullcahuaman, C. Castañeda, C. Munive, B. Muñante, J. Abugattas, H. Guerra, I. Otoya, V. Acuña, S. Gruber. Brca1/2-tested breast and ovarian cancer patients in peru: clinical and genomic features abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-03-22.