BCL9 and cancer: We first evaluated whether in fetal‐like HB cell lines, the partial deletion of CTNNB1 exon 4 could alter the capability of β‐catenin to interact with BCL9 and BCL9L, which are established co‐activators of the Wnt pathway important to specify a stem cell‐like phenotype in cancer cells (Brembeck et al, 2004; Deka et al, 2010).