ESR1 and endocervical adenocarcinoma: Classification is further complicated by the histopathological overlap between endocervical adenocarcinoma and endometrial adenocarcinoma, which requires the use of p16, estrogen receptor (ER), progesterone receptor (PR), and carcinoembryonic antigen (CEA) immunohistochemical markers for differentiating primary cervical malignancies from metastatic or endometrial tumors [16].