Age-related mutational signature negatively associated with immune activity and survival outcome in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is characterized by broad genomic and transcriptional heterogeneity and results in a worse prognosis than other breast cancer types. Here, we integrated genomic and transcriptomic data combined with clinicopathologic information from 538 patients with TNBC and identified four novel significantly mutated genes (SMGs), namely, KDM6A, CD86, RBM47, and IFNGR1. A mutational signature (known as age-related signature 1) featured by enrichment of C > T mutations at NpCpG trinucleotides was associated with worse survival in TNBC (HR, 1.76 [95% CI, 1.07-2.90]; P = .025). We also analyzed gene transcriptomic profiles of TNBC samples and identified immune regulation-related gene pathways (e.g., antigen processing presentation and interferon signaling), and the cell cycle was significantly altered in samples with different signature 1 activity groups. The analysis further revealed that signature 1 was associated with decreased tumor immunogenicity and immunocyte infiltration in TNBC. This negative correlation was also observed in lung adenocarcinoma and prostate cancer samples. Furthermore, we found that patients with mutational signature 1 were markedly associated with decreased tumor mutation burden, even after controlling for age, grade, histological type, lymph node status, mutations in BRCA1/2 and ATR, and APOBEC and homologous recombination repair deficiency signatures (OR, 0.19 [95% CI, 0.11-0.32]; P < .001). Overall, this study identified previously unreported SMGs and re-annotated that age-related signature 1 was associated with a weakened immune microenvironment and predictive of poor survival in TNBC, offering opportunities to stratify patients into optimal treatment plans based on genomic subtyping.