BRCA2 and neoplasm: To begin to identify possible relevant mechanisms that drive resistance, we first carried out a detailed histopathological analysis of olaparib-naïve and relapsed/resistant tumours from the BlgCre Brca2/Tp53-mutant mouse mammary model, based on H&E appearance and immunohistochemical staining for KRT14, KRT18, TP63 and VIM and using our previous histotype classification system [14, 15] (Tables 1 and 2; Figures 1–4).