ESR1 and neoplasm: Third, it has been widely accepted that AC is defined by a combination of morphologic (apocrine morphology in > 90% of tumor cells) and immunohistochemical (ER‐ and PR‐negative and AR‐positive) characteristics.17 However, the AR status was not an essential criterion for the diagnosis of AC; therefore, its expression was not recorded routinely in the SEER database.