ESR1 and breast cancer: Similar TREM1 expression patterns were observed among cell types grouped by tumor subtype (TNBC, n=13; ER+, n=15; HER2+ (ER+/-), n=3) (Supplemental Figure 4), and within tumors of individual patients (Supplemental Figure 5), confirming that TREM1 expression in breast cancer is a predominantly myeloid phenomenon.