[Analyzing the impact of chemotherapy on cellular heterogeneity and identifying potential therapeutic targets in breast cancer patients via single-cell RNA sequencing].

Objective: Profiling tumor cell heterogeneity before and after chemotherapy in breast cancer patients to delineate the cellular evolutionary trajectory at single-cell resolution, thereby identifying potential targets for intervention. Methods: Using a case-control study design, a female patient with breast cancer admitted to the Department of Breast Surgery, The First Affiliated Hospital of Hunan University of Chinese Medicine in September 2020 was enrolled as the subject. Fresh tumor tissue samples, collected both before and after chemotherapy, were subjected to single-cell RNA sequencing to assess transcriptomic profiles and observe the impact of chemotherapy on the intratumoral microenvironment. Specifically, a pre-chemotherapy biopsy sample was obtained in June 2020, and a post-chemotherapy surgical resection sample was obtained in September 2020. Pathological diagnosis confirmed Grade Ⅲ invasive ductal carcinoma for both samples, with a molecular subtype of Luminal B. Results: A significance threshold of |log₂FC|>2 and a P-value <0.05 were set to define statistically significant differences for subsequent bioinformatic analysis. Sequencing data revealed that a total of 8 599 cells were profiled in this study, with 4 180 (48.6%) and 4 419 (51.4%) cells derived from pre- and post-chemotherapy tumor tissues, respectively. It characterized the cellular composition of the tumor microenvironment and identified 13 distinct cell clusters. These included basal cells, pericytes, plasma cells, T cells, B cells, fibroblasts, endothelial cells, NK cells, mast cells, epithelial cells, macrophages, cycling cells, and plasmacytoid dendritic cells. Signaling pathways and transcription factors associated with these cell clusters were subsequently analyzed and subjected to enrichment analysis. Furthermore, this study delineated the precise cellular architecture and developmental trajectories of breast cancer before and after chemotherapy. It also predicted that the APOD, ELN, and F2R genes may play pivotal roles in disease progression. Conclusion: This study utilized single-cell RNA sequencing to analyze intra-tumoral cellular heterogeneity in a breast cancer patient before and after chemotherapy. The findings may provide a clinically informative direction for identifying novel potential therapeutic targets during chemotherapy, prior to primary tumor resection.