ESR1 and neoplasm: Immunohistochemically, tumor cells were diffusely positive for tumor protein 53 (p53) (Fig. 2e, f), caudal-type homeobox 2 (CDX2) and special AT-rich sequence-binding protein 2 (SATB2) (Fig. 3), positive for cytokeratin 20 (CK20) (Fig. 3) and negative for cytokeratin 7 (CK7), androgen receptor (AR) (Fig. 3), gross cystic disease fluid protein 15 (GCDFP-15), estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2).