ESR1 and invasive ductal breast carcinoma: Single-cell RNA sequencing (scRNAseq) of an ER+/HER2 + invasive ductal carcinoma sample further confirmed that BRRIAR expression was largely restricted to tumor cells (16.5%), with only sparse expression detected in platelets (5.5%), CD4+/CD8 + T-cells (3.8%), and other cell types (Fig. 1f, g and Supplementary Fig. 1e-g and Supplementary Tables 3–5).