Interestingly, this study reported lower frequency of ESR1 mutations in locoregional recurrences versus advanced metastases at an AF > 1% and recent data has emerged regarding a pro-metastatic phenotype of ESR1 variants [68]—suggesting locoregional recurrences may have a lower frequency of ESR1 variants versus distant disease. Here, ESR1 is linked to atrial fibrillation.