(A) Proteomic analysis of 59 immune-related proteins in TCGA samples of PAM50-defined intrinsic and hormone receptor subtypes, including 19 TNBC, 13 luminal A, 17 luminal B, and 10 Her2⁺ breast tumors. (B) Heatmap and hierarchical clustering are based on the expression levels of the 309 immune-related proteins — differentially expressed in 4 breast cancer types. Each column represents a sample; each row represents a protein. The log₂ relative protein expression scale is depicted on the top left. (C) Volcano plots showing the immune-related protein expression changes in 2 TNBC patient cohorts. Each circle represents 1 protein. The log fold change is represented on the x-axis. The y-axis shows the FDR adjusted log₁₀ of the P value. (D) CD73 and PD-L1 expression density in 2 TNBC groups were calculated based on log₂ relative protein expression. (E) mRNA analysis of immune-relevant proteins in 37 specimens from patients with TNBC from the GEO database. The genes (rows) are sorted according to the difference between the average mRNA levels in breast cancer types. (F) Breast cancer specimens TMA stained with an anti-CD73 antibody and representative pictures of different breast cancer subtypes are shown. Scale bars: 100 μm.(G) Quantified TMA consisting of luminal A, luminal B, Her2⁺, and TNBC samples immune stained for CD73. (H) The expression of CD73 in normal human mammary epithelial cells and various subtypes of breast cancer cells was detected by immunoblotting using an anti-CD73 antibody. (I) Kaplan-Meier curves using multivariable Cox proportional hazard model for the corresponding CD8⁺ T cells and CD73 expression. A total n = 1,100 breast cancer patients were included in the study, with 20 cases having missing data. The analysis was performed on the remaining 1,080 patients, of whom 153 had died, and Kaplan-Meier curves were subsequently plotted. Low- and high-expression groups refer to patients with expression levels lower and greater than the 50^th percentile, respectively. **P < 0.01, ***P < 0.001, and ****P < 0.0001, statistical significance was determined by 1-way ANOVA with Tukey’s multiple comparisons test for immunostaining using n = 110 breast samples.