NUMB and breast cancer: Pece et al. (2004) found that Numb protein was completely lost or reduced in ∼50% of all breast cancers analysed, through ubiquitination and proteasomal degradation. Numb levels and tumour grade were inversely correlated, which was corroborated by another study that identified Numb loss as a determinant in aggressive and poor prognosis tumours. Collectively, these studies emphasise the importance of Numb as a tumour suppressor in the breast (Colaluca et al., 2008).