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Breast cancer, accounting for 17.1% of the female cancers, is the most frequently diagnosed malignancy among women in China. Current treatment strategies based on the breast cancer subtype have remarkably improved the prognosis, however, obstacles remain. It’s of great importance to elucidate problems, including the tumor heterogeneity, metastases and therapeutic resistance, to promote therapeutic efficacy. Single-cell RNA sequencing is a novel method that enables unbiased, high-throughput and high-resolution transcriptomic analysis at the single-cell level. It could profile intratumor gene expression features at single-cell resolution and improve our understanding of breast cancer. This review illustrated the application of single-cell RNA sequencing in breast cancer from diverse aspects to obtain further knowledge of this emerging technology and provided new insights into breast cancer research.

Background: Triple‐negative breast cancer (TNBC) displays high heterogeneity. The majority of TNBC cases are characterized by high Ki‐67 expression. TNBC with low Ki‐67 expression accounts for only a small fraction of cases and has been relatively less studied. Methods: This study analyzed a large single‐center multiomics TNBC data set, combined with a single‐cell data set. The clinical, genomic, and metabolic characteristics of patients with low Ki‐67 TNBC were analyzed. Results: The clinical and pathological characteristics were analyzed in 2217 TNBC patients. Low Ki‐67 TNBC was associated with a higher patient age at diagnosis, a lower proportion of invasive ductal carcinoma, increased alterations in the PI3K‐AKT‐mTOR pathway, upregulated lipid metabolism pathways, and enhanced infiltration of M2 macrophages. High Ki‐67 TNBC exhibited a higher prevalence of TP53 gene mutations, elevated nucleotide metabolism, and increased infiltration of M1 macrophages. Conclusions: We identified specific genomic and metabolic characteristics unique to low Ki‐67 TNBC, which have implications for the development of precision therapies and patient stratification strategies. [ABSTRACT FROM AUTHOR]