ESR1 and neoplasm: The primary staining of tumor sections was performed with a highly specific antihuman antibody against PR (Dako FLEX monoclonal mouse antihuman PR; Clone PgR 636) that enhanced the sensitivity of the detection, thereby grading the majority of tissue samples as PR-luminal (ER+/PR−/HER2−) and triple-negative (ER−/PR−/HER2−) subtypes, respectively (Figure 4B).