BRCA1 and cancer: Notably, there is also a tendency in BRCA1/2 mutation carriers who have had multiple tumours to show higher rates of HER2 positivity in later-onset lesions (78%), with a case report in a BRCA1mut carrier showing loss of the BRCA1mut gene, without inactivation of the BRCA1wt gene presenting with an HER2-amplified cancer [44].