ERBB2 and cancer: Nevertheless, there is a reduced incidence of HER2-positive breast cancers in BRCA1- and BRCA2-associated tumours, with a recent pooled analysis of a total of 21,083 BRCA1 and BRCA2mut cancers from 73 studies [41], showing mean HER2-positive rates of 8.3% and 10.3%, respectively (combined 9.1%, 95% CI interval 7.3–11.2%).