The clinical characteristics of the cohort represent the expected distribution for early breast cancer in Sweden (Table 1): the median patient age at diagnosis was 64 years; 84.6% were ER positive; 71.7% progesterone receptor (PR) positive; 12.9% had HER2 amplification; 35.5% were positive for tumor spread to at least 1 lymph node at the time of surgery; 15.0% were Nottingham histological grade 1, 46.9% grade 2, and 36.1% grade 3. This evidence concerns the gene ESR1 and breast cancer.