ESR1 and breast cancer: In contrast, Wagner et al. deciphered single-cell proteomics of tumor and immune cells in patients with BC subtypes, thus providing an opportunity to portray the ecosystem differences, particularly for immune cell distinctions, among different BC subtypes.191 Notably, they observed a higher frequency of Tregs and exhausted T cells in high-grade estrogen receptor-negative (ER−) and ER-positive (ER+) tumors, probably indicating the cellular basis of better responses to ICIs for the ER− subtype and a subset of high-grade ER+ patients.