Endoscopic biopsy and histopathological examinations are particularly important for the diagnosis, while immunohistochemistry is considered to be the gold standard for differentiating between metastatic and primary cancers.[43,44] ER and PR, 2 important indicators of endocrine therapy and prognostic indicators of breast cancer, are the most frequently examined markers in such cases. Here, ESR1 is linked to breast carcinoma.