Mutations affecting NOTCH2 (6%), NOTCH3 (9%), DNER (3%), EP300 (3%), and CUL1 (3%) were found in MBCs, whereas NOTCH4 (2%) alterations were only detected in UCSs (Fig. 3D, Fig. S1b). Here, CUL1 is linked to maternal uniparental disomy of chromosome 20.