To understand how Notch1 loss alters tumor growth, we sequenced tumors from Notch1−/− epithelium, finding they share the same driver mutation, Atp2a2, (6/7 tumors), as the tumors from Notch1+/+ epithelium (17/17 tumors) (Extended data Fig. 8a–c and Supplementary Tables 20 and 26)35,36. Here, NOTCH1 is linked to neoplasm.