PTEN and cancer: This observation is in accordance with the hypothesis that hemizygous loss of PTEN with haplo-insufficiency of the remaining allele leads to genomic instability and cancer development as shown by in vivo studies on knockout PTEN mice (Di Cristofano et al, 1998; Kwabi-Addo et al, 2001; Shen-Li et al, 2011), while complete inactivation accelerates tumour dedifferentiation, progression and metastases (Verhagen et al, 2006; Schmitz et al, 2007).