The BEACCON study aimed to address the lack of power of previous studies to identify additional BC predisposition genes by performing extensive sequencing in 12,000 women (11,511 analysed following exclusions) and further enhancing power by using an ‘extreme phenotype’ design with enrichment of familial non-BRCA1/2 cases, compared with a control population of older women with ongoing confirmation of cancer-free status at June 2019. The gene discussed is BRCA1; the disease is breast cancer.