Objective <p>This study was aimed to screen and validate key genes associated with Ki-67 expression and evaluate their prognostic significance in patients with triple-negative breast cancer (TNBC).</p> Methods and results <p>RNA sequencing data and clinical characteristics were obtained from the Fudan University Shanghai Cancer Center (FUSCC) database. A Cox regression model and bioinformatic analyses were employed to identify Ki-67–related prognostic genes. Candidate genes were further validated using the Kaplan-Meier Plotter database and patient specimens from our medical center. A total of 241 differentially expressed genes between high and low Ki-67 expression groups were initially identified through Gene Ontology functional analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment. Further analysis revealed that CCNA2, a Ki-67–related gene, was an independent risk factor for overall survival. Patients with high-risk scores exhibited significantly higher mortality rates than those with low-risk scores. Moreover, immunohistochemistry analysis showed that high CCNA2 protein expression was significantly associated with histological grade and recurrence or metastasis within 3 years after surgery (all <i>P</i> &lt; 0.05).</p> Conclusions <p>CCNA2 overexpression may contribute to tumorigenesis and serve as a potential prognostic biomarker indicating poor outcomes in TNBC.</p>