Abstract P3-03-17: Genetic Profiles and Precision Medicine in Adolescent and Young Adult Chinese Women with Breast Cancer: A Comprehensive Study

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Abstract Background: Breast cancer is a major health concern worldwide, especially among Adolescent and Young Adult (AYA) women who face unique biological and clinical challenges. AYA breast cancer patients often present with aggressive subtypes, requiring specific treatment considerations such as fertility preservation and long-term survivorship. This study aims to analyze the genetic characteristics of AYA Chinese women with breast cancer, focusing on genomic alteration profiles and their correlation with clinical outcomes, to provide precise treatment guidance. Patients and Methods: We analyzed tumor and matched blood samples from 202 young Chinese breast cancer patients (≤39 years) diagnosed between 2014 and 2024. Targeted next-generation sequencing was conducted on formalin-fixed paraffin-embedded (FFPE) or fresh tumors. Personalized ctDNA assays were used for Minimal Residual Disease (MRD) monitoring to detect early recurrence and guide treatment. Experiments were performed in a CAP/CLIA-certified laboratory. Results: The study cohort had a median age of 35 years (range 18-39). Among them, 48.02% (97/202) were in stages I-II, 42.08% (85/202) in stages III-IV, and 9.9% (20/202) had unclear staging. Molecular subtypes included 28.71% (58/202) HER2+, 32.67% (66/202) ER+/PR+/HER2-, and 28.22% (57/202) triple-negative breast cancer (TNBC). The top 5 mutated genes in TNBC were TP53 (86%,49/57), PIK3CA (14%,8/57), RB1 (14%,8/57), PTEN (10.5%,6/57), and CDKN2A (8.8%,5/57). For HER2+ patients, they were ERBB2 (86%, 50/58), TP53 (64%,37/58), PIK3CA (28%,16/58), CCND1 (10.3%,6/58), and BRAF (5.2%,3/58). ER+/PR+/HER2- patients had TP53 (36%,24/66), PIK3CA (35%,23/66), CCND1 (20%,13/66), PTEN (12.1%,8/66), and AKT1 (7.6%,5/66). Among the 58 HER2+ cases, 49 have ERBB2 somatic gene amplification, while 5 in 49 co-occuring point mutations. Germline testing was performed on 197 patients, with 11.67% (23/197) showing pathogenic/suspected pathogenic mutations in BRCA1/2. A case study of a 34-year-old HER2+ patient demonstrated the value of precision medicine and MRD monitoring. MRD testing detected recurrence two months earlier than imaging. Treatment with the HER2-targeted drug DS-8201 led to complete response, maintained over four consecutives negative MRD tests. Conclusions: Our findings underscore the diverse molecular subtypes and significant genetic mutations among young Chinese breast cancer patients, highlighting the necessity of personalized treatment strategies. Incorporating precision medicine and MRD monitoring can significantly enhance early recurrence detection and improve overall treatment outcomes. Future research should focus on validating these findings and developing tailored strategies in larger cohorts. Citation Format: Qing Hao, Fei Pang, Chengyi Wang, Hongrui Zhou, Aodi Wang, Hui Chen. Genetic Profiles and Precision Medicine in Adolescent and Young Adult Chinese Women with Breast Cancer: A Comprehensive Study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P3-03-17.

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