Abstract N6-methyladenosine (m6A) is a common RNA modification on eukaryotic mRNA and several m6a regulatory proteins, which plays a crucial part in breast cancer. But the copy number variations (CNVs) for m6a regulatory proteins and their role in pathogenesis and progression in breast cancer is still unclear. By analyzing the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) and the cancer genome atlas (TCGA database), we screened CNVs of ten m6A regulatory genes, including YTHDF3, YTHDF1, FTO, YTHDC1, ALKBH5, METTL3, WTAP, METTL14, YTHDF2, YTHDC2. Among them, YTHDF3 and YTHDF1 amplification had higher alteration rates among ten m6A regulatory genes. YTHDF1 and YTHDF3 amplification resulted in higher mRNA expression (P<0.001). We found that YTHDF1 and YTHDF3 amplification presented a high correlation with worse cinlicopathological characteristics and overall survival (OS) in breast cancer patients. COX regression analysis showed YTHDF1 amplification was an independent risk factor for 10-year OS in breast cancer (HR=1.549, 95% CI: 1.408-1.705, P<0.001, Table). Moreover, GSEA analysis revealed the downstream target of YTHDF1 may be related to MYC signaling regulation and T cell differentiation. In conclusion, we illustrated genetic alteration of m6A regulatory genes in breast cancer patients and found significant relationship between YTHDF1 amplification and worse clinical characteristics, indicating it a potential target for breast cancer treatment in epigenetic modification. Univariate and multivariate Cox proportional hazard analysis for 10-year overall survivalUnivariateUnivariateHR95% CIP valueHR95% CIP valueNode status1.7181.566-1.885<0.0011.5491.408-1.705<0.001Tumor Size1.0161.013-1.019<0.001ER status0.6200.530-0.725<0.0010.5260.440-0.629<0.001PR status0.6120.531-0.707<0.001HER2 status1.7471.445-2.112<0.0011.5171.234-1.866<0.001Age1.0241.018-1.030<0.0011.0331.026-1.039<0.001YTHDF11.8111.419-2.313<0.0011.5491.408-1.705<0.001 Citation Format: Cheukfai Li, Guochun Zhang, Yulei Wang, Bo Chen, Kai Li, Li Cao, Chongyang Ren, Lingzhu Wen, Minghan Jia, Hsiaopei Mok, Jianguo Lai, Weikai Xiao, Xuerui Li, Ning Liao. YTHDF1 amplification associates with clinicopathological featuresand predicts worse survival in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5912.