The PTEN inactivation may be related with gene mutations (<5% of sporadic BC) (Vanhaesebroeck and Alessi, 2000) or promoter hypermethylation (20%) (Saal et al, 2005), resulting in PTEN loss that occurs in about half of the tumours (Nagata et al, 2004; Lerma et al, 2008; Esteva et al, 2011; Razis et al, 2011). The gene discussed is PTEN; the disease is breast cancer.