The index case (family 5440; PID: III‐6) was diagnosed with BC (invasive carcinoma of no special type (invasive ductal carcinoma, not otherwise specified), clinical stage IIA, estrogen receptor (ER) negative, progesterone receptor (PR) negative, and human epidermal growth factor receptor 2 (HER2) negative) at age 49, and screened negative for pathogenic and likely pathogenic variants in moderate‐ and high‐risk cancer susceptibility genes. Here, ESR1 is linked to breast cancer.