LAUSR

BACKGROUND Tumor-associated tissue eosinophilia (TATE) has been associated with outcomes in a variety of solid tumors; however, its role in breast cancer is not well defined. We hypothesized that tumor-associated tissue eosinophilia is associated with a high mutation and neoantigen load, and we assessed its correlation with cancer outcomes. METHODS The Cancer Genome Atlas was analyzed for eosinophil signatures in breast cancer specimens. Descriptive analyses were performed, including the tumor-infiltrating cell composition using CIBERSORT, cytolytic activity score, and gene set enrichment analysis. Overall survival and disease-free survival were calculated using the Kaplan-Meier method. RESULTS Out of 1069 cases analyzed, 40 (3.7%) had tissue eosinophils (the tumor-associated tissue eosinophilia group). Tumor-associated tissue eosinophilia was noted in 32.5% luminal, 5% HER2-positive, and 15% triple-negative breast cancer subtypes. The single nucleotide variant-neoantigen load was significantly higher in the tumor-associated tissue eosinophilia group (P = .005), with a higher nonsilent mutation rate (P = .01). The tumor-associated tissue eosinophilia group had lower cytolytic activity (P = .02) but had enriched MYC-targeted (P = .002), E2F-targeted (P = .04), deoxyribonucleic acid repair (P = .03), and unfolded protein response gene sets (P = .05). Tumor-associated tissue eosinophilia was associated with a trend toward improved disease-free survival (P = .06) but presented no differences in overall survival (P = .56). CONCLUSION Tumor-associated tissue eosinophilia was noted in 3.7% of breast cancers and was associated with a higher single nucleotide variant-neoantigen load and nonsilent mutation rate, similar to that of tumor-infiltrating lymphocytes in the triple-negative subtype. However, a lower cytolytic activity score and enriched cell proliferation-related gene sets implicate different roles for tumor-associated tissue eosinophilia than for tumor-infiltrating lymphocytes.