e13126 Background: Triple negative breast cancer (TNBC) represents 15% of all breast cancer cases and is one of the most aggressive forms of breast cancer with a poorer prognosis. Due to the lack of receptors, TNBC is not amendable to hormonal or anti-HER2 therapies and current gene expression arrays have limited clinical utility in TNBC. The identification of biomarkers associated with TNBC may aid in elucidating the underlying biological mechanisms of this disease and may also have implications for risk stratification, diagnosis, and prognosis of TNBC. The purpose of this study was to investigate the association between markers of biological aging and time to relapse in TNBC. Methods: DNA methylation and clinical data from a publicly available dataset (GSE141441) were used in this analysis. Breast tissue specimens in female TNBC patients who received (n=56) and who did not receive (n=110) chemotherapy underwent DNA methylation profiling using the Illumina Infinium HumanMethylation450K BeadChip. Five DNA methylation-based biological age metrics were calculated: intrinsic epigenetic age acceleration (IEAA), extrinsic epigenetic age acceleration (EEAA), PhenoAge acceleration (PhenoAA), GrimAge acceleration (GrimAA), and DunedinPACE (Pace of Aging Calculated from the Epigenome). Multiple linear and quantile regression analyses were performed to examine the association between the aging metrics and time to TNBC relapse. Interaction and stratified analyses by Ki-67 was additionally performed. Results: After adjusting for chronological age, GrimAA ( P=0.024) and DunedinPACE ( P=0.019) were negatively associated with time to relapse among patients who did not receive chemotherapy. Specifically, a 1-year increase in GrimAA and 1 unit increase in the pace of aging were associated with a 1.77-month and a 53.62-month shorter relapse of TNBC, respectively. Additionally, Ki-67 significantly modified the association between IEAA ( P=0.023) and DunedinPACE ( P=0.035) among patients who received chemotherapy with a 2.75- and a 42.17-month shorter relapse of TNBC among those with a Ki-67 index greater than 50% per unit increase in IEAA and DunedinPACE, respectively. Conclusions: We observed DNA methylation markers of biological age were associated with time to relapse in TNBC patients and these associations were modified by Ki-67. These biomarkers may have prognostic utility in TNBC relapse and potentially, may aid in oncological precision medicine efforts for personalized treatment regimens and surveillance. [Table: see text]