ESR1 and invasive ductal breast carcinoma: PMBC has distinct clinicopathological and molecular features, including higher estrogen receptor (ER) and progesterone receptor (PR) expression, greater likelihood of human epidermal growth factor receptor-2 (HER2)-negative status, lower grade, and lower risk of nodal metastasis [3–5], which all contribute to better outcomes compared to invasive ductal carcinoma (IDC); indeed, the 10-year disease-free survival rate is > 90% [6–12].