To investigate NUMB hyper‐degradation, we selected suitable in vitro models from a screening of established BC cell lines: NUMB‐deficient MDA‐MB‐361 cells expressing low NUMB levels rescuable by treatment with the proteasome inhibitor bortezomib (BTZ), and NUMB‐proficient MDA‐MB‐231 cells exhibiting high basal NUMB levels insensitive to BTZ (Figure2a). Here, NUMB is linked to breast cancer.