ESR1 and neoplasm: Next, we further detected that the PD-1 expression was upregulated in tumor tissues, the ER-negative group (ER-) and PR-negative group (PR-) in both TCGA and METABRIC datasets, while upregulation of PD-1 in the HER2-positive group was only observed in the METABRIC dataset (Figures 2A–F).