ESR1 and neoplasm: To better characterize the native tumor immune microenvironment of human breast cancer, we applied a CITE-Seq panel of 97–157 antibodies (157 in 5 samples, 97 in one; Table S1) to 6 breast cancer samples, representing all major clinical subtypes: Luminal (estrogen receptor-positive (ER+) and progesterone receptor -positive/negative (PR+/−), human epidermal growth factor receptor positive (HER2+) and Triple negative breast cancer (TNBC) (Table S2).