Abstract PO1-10-01: Racial/Ethnic Disparities in Rates of Pathological Complete Response and Survival in Patients with Inflammatory Breast Cancer

Abstract Radiation Therapy Toxicities and Survival Outcomes in Monoallelic ATM Variant Carriers with Non-Metastatic Breast Cancer: A Retrospective Analysis Rayan Bensenane1 MD, Arnaud Beddok1,2,3 MD, Nadine Andrieu4 PhD, Fabienne Lesueur4 PhD, Eve Cavaciuti 4 MSc, Dorothee Le Gal4 MSc, Eon-Marchais Severine4 PhD, Dominique Stoppa Lyonnet 5MD PhD, Youlia Kirova1 MD 1. Institut Curie, PSL Research University, Radiation Oncology Department, Paris/Saint-Cloud/Orsay, France. 2. Gordon Center for Medical Imaging, Massachusetts General Hospital, Harvard Medical School, 125 Nashua St., Boston, MA, 02114, USA 3. Institut Curie, PSL Research University, University Paris Saclay, Inserm LITO U1288 Orsay, France 4. Inserm, U900, Institut Curie, PSL Research University, Mines ParisTech, Paris, France 5.Department of Genetics, Institut Curie; Inserm U830, Institut Curie; Paris-Cité University Abstract (characters: 2952; max 3400 characters, not include spaces) Background: The Ataxia-Telangiectasia Mutated (ATM) gene, involved in the repair of DNA double-strand breaks, can contribute to radiosensitivity when a bi-allelic variant is present and lead to Ataxia-Telangiectasia syndrome. Moreover, monoallelic ATM pathologic variant (PV) carriers, especially women, has an estimated occurrence rate of 0.5-1% globally and face a 2 to 3-fold increased risk of developing breast cancer. Despite evidence of in vitro radiosensitivity in cells derived from monoallelic variant carriers, there is a dearth of patient studies examining the risk of radiation-induced toxicity. This study aims to explore radiation therapy (RT) toxicities in non-metastatic breast cancer women carrying a germline monoallelic ATM variant, compared to non-carriers. Methods: A retrospective study was conducted on patients treated at Institut Curie, Paris from 1999 to 2014 and participating to CoF-AT (a French national study) and GENESIS database. ATM variant screenings encompassed both PV and non-PV, with toxicities evaluated using CTCAE v.5. Variants were classified as pathogenic, variant of unknown significance (VUS), or benign. Follow-up started from age/date at breast cancer to acute, late toxicities, disease recurrence or last news. Survival and toxicity comparisons were made using Kaplan-Meier survival analysis and Chi-square tests, respectively, with a significance level of α set at 0.05. Results: Among 50 patients, nine were ATM variant carriers (3 PV/5 VUS/1 benign), and 41 were non-carriers. Most patients had no smoking history (68%), and invasive ductal carcinoma was the predominant diagnosis (82%). The majority underwent breast-conservative surgery (80%), and the dominant RT techniques were 3D-Conformational Radiation Therapy (70%) and Isocentric Lateral Decubitus (30%). The median RT dose was 50 Gy over an average period of 36.5 days. With a median follow-up of 12 years post-diagnosis, no significant difference in acute dermatitis, esophagitis, lymphedema, cutaneous fibrosis, telangiectasia, or heart disease was observed between the groups. Analysis of overall survival (OS) showed a 5-year OS of 98%, decreasing to 89% at 10 years. For ATM variant carriers, the OS at 5, 10, and 15 years was 100%, 89%, and 89%, respectively, similar to non-carriers. Kaplan-Meier analysis revealed no significant differences in 5, 10, and 15-year overall survival, progression-free survival, local failure-specific survival, and contralateral breast cancer rates between the groups. Conclusion: In non-metastatic breast cancer patients, monoallelic ATM variant carrier status does not significantly influence acute or late RT toxicities and survival outcomes. These findings, derived from a small cohort, highlight the need for prospective studies for further validation. Table: Acute and Late Toxicities Post-Radiation Therapy in Monoallelic ATM Variant Carriers vs Non-Carriers Citation Format: Rebecca Zasloff, Samantha Thomas, Kendra Parrish, Astrid Botty van de Bruele, Gayle DiLalla, Maggie DiNome, Laura Rosenberger, Hannah Woriax, E Shelley Hwang, Jennifer Plichta, Akiko Chiba. Racial/Ethnic Disparities in Rates of Pathological Complete Response and Survival in Patients with Inflammatory 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 PO1-10-01.