Examination of sections stained with haematoxylin and eosin (H&E) from the fragment-derived MMTV-NIC PTEN+/− tumours confirmed the presence of highly mitotic, grade 3 carcinomas, which were indistinguishable from tumours that developed in the parental MMTV-NIC PTEN+/− model (Fig. 2A). Here, PTEN is linked to carcinoma.