Abstract PS3-03-07: Breast and Ovarian Cancer Genomic Risk Assessment: 10-Year Experience from a High-Risk Program

Abstract Breast cancer (BC) is one of the most common cancers among women in both Peru and worldwide. Ovarian cancer (OC), due to the difficulty of early detection, also represents a significant public health concern in the country. In recent years, genetic testing has become essential for identifying individuals at high risk for hereditary cancer predisposition syndromes, guiding decisions related to prevention, early detection, and treatment. In Peru, the use of genetic testing is still developing. This work presents an inter-institutional collaborative experience that has facilitated access to genetic testing and contributed to the implementation of a multidisciplinary care system for managing high-risk patients. The main objective of this study is to identify the genomic profile of patients with breast and/or ovarian cancer and to evaluate the clinical impact of genetic testing on cancer management. Methods: This study includes individuals diagnosed with breast and/or ovarian cancer who were referred for Medical Genetics evaluation at the Instituto Nacional de Enfermedades Neoplásicas (INEN) between August 2013 and March 2020. Participants met criteria for inclusion in the inter-institutional protocol INEN13-48 on hereditary cancer and underwent genetic testing at City of Hope (IRB #96144). Results and Discussion: We recruited 1577 patients; 99. 3% were females (n=1566/1577) with the initial diagnosis of BC (89. 4%. n=1401/1566), OC (8. 5%. n=133/1566) and BC/OC (2%. n=32/1566) ; 0. 7% were males (n=11/1577) all BC. Of all the individuals, 46. 8% (n=738/1577) had the first diagnosis under 40yo; 36. 1% (n=570/1577) was between 41-50yo. 13. 4% (n=212/1577) had a LP/P variant in an actionable gene with management guidelines for at least one cancer type; 0. 8% (n=12/1577) had a LP/P variant in an non actionable gene; 34. 5% (n=545/1577) had a BRCA1/BRCA2 panel with no variant detection and 51. 2% (n=808/1577) had an extended panel with no variant detection. The most frequent LP/P variants in actionable genes were 53. 8% (n=114/212) in BRCA1 and 24% (n=51/212) in BRCA2; 1% (n=2/212) had more than one LP/P variant (BRCA1/BRIP1 and BRCA1/BRCA2). The detection rate of LP/P variant in BC was 12% (n=170/1401) in BC, 19. 5% (n=26/133) in OC and 50% (n=16/32) in B/OC. The most frequent LP/P variants were BRCA1 (NM₀07294. 4): c. 68₆9del (p. Glu23ValfsTer17) (6%: n=13/212) and BRCA2 (NM₀00059. 4): c. 1219CT (p. Gln407Ter) (4% n=8/212). 9% (n=1/11) of the male patients, had a variant in BRCA2 gene. All 212 patients were evaluated in clinical genetics. Over 10 years of follow-up, 72% (n=152) received recommendations for high-risk breast cancer (BC) management and 54% (n=115) for ovarian cancer (OC) ; the rest did not due to disease progression or geographic barriers. Among those at high BC risk, 34% (n=60) began imaging-based surveillance, 26% (n=40) underwent unilateral/bilateral risk-reducing mastectomy (RRM) —with 10% (n=4) diagnosed with new BC—and 34% (n=52) declined recommendations. In the high OC risk group, 18% (n=21) had prior ovarian surgery, 49% (n=56) underwent risk-reducing salpingo-oophorectomy (RRSO) —with 2 OC diagnoses—and 23% (n=27) declined. As of now, 36. 7% (n=78) have died and 17% (n=37) are lost to follow-up. Conclusion: The importance of ensuring access to genetic studies, in addition to the recognition of genetic predisposition syndromes to cancer is paramount. In this cohort we identified that 13% of individuals had an LP/P in an actionable gene, similar to other cohorts. This information support the needs of long-term financing, not only to access to genetic testing, but helps us to improve the access to multidisciplinary high-risk management in our institution considering the geographical and economic barriers in our country. Citation Format: P. Mora, M. Acosta, J. Herzog, N. Valdiviezo, L. Reynaga, J. Abugattas, Y. Sullcahuaman, T. Vidaurre, S. Neciosup, J. Dunstan, H. Gómez, I. Otoya, Z. Morante, V. Acuña, A. López, S. Gruber. Breast and Ovarian Cancer Genomic Risk Assessment: 10-Year Experience from a High-Risk Program 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 PS3-03-07.