ESR1 and breast cancer: When differentiating from other metastatic adenocarcinomas, in addition to selecting adenocarcinoma markers (MOC31, BerEP4, BG8, B72.3, CEA), organ‐specific markers such as estrogen receptor (ER), progesterone receptor (PR), GCDFP15, and mammaglobin for breast cancer, PAX8, PAX2, RCC, CD15 for renal cancer, and PAX8, ER, PR for ovarian cancer should also be included.