ESR1 and neoplasm: Both in tumor and stromal tissue compartments of matched samples, CD4 + T-cells were the most abundant cell type (mean cell density: 1104 and 909 cells/mm2, respectively), followed by CD68 + macrophages (mean cell density: 114.2 and 278.3 cells/mm2, respectively) (Fig. 1d and Supplementary Table 1), with higher mean cell densities observed in ER-negative compared to ER-positive tumors (Supplementary Fig. 1a).