In this study, we identified the differentially expressed genes (DEGs) in HER2+ BC and ERGs, determined the exosome prognostic genes (EPGs) via Kaplan–Meier (KM) analysis, LASSO Cox regression, and random forest model, performed the clustering analysis, mutation feature analysis, enrichment analysis, and determined the relationship between EPGs and the immune microenvironment using a single cell RNA-sequencing dataset containing five clinical samples. The gene discussed is ERBB2; the disease is breast cancer.