CTNNB1 and maternal uniparental disomy of chromosome 20: We also reported that MBCs frequently harbored mutations in the Wnt pathway.9 Consistent with our observations from whole-exome sequencing analysis of MBCs,9 we did not identify expressed mutations affecting CTNNB1. We did, however, detect an expressed frameshift SMAD4 mutation and an expressed missense TCF7L2 mutation.