In a single-cell study of the breast tumor microenvironment, TREM2+ TAMs were found to be a kind of recruited or resident M2-type macrophages expressing genes like SPP1, APOE, and C1Q, as in our study, suggesting that the TREM2+ TAM subpopulation may be functionally closer to M2 polarized macrophages (55). Here, APOE is linked to breast neoplasm.