PTEN and carcinoma: [37]). The critical radius for nucleation and the final PIP-patch size are functions of the PI3K/PTEN ratio [37]. This fact suggests that the precise amount of PI3K and PTEN is a critical parameter for the establishement of epithelial polarity, providing an explanation for the experimental observation that deletion of a single PTEN allele can interfere with epithelial cell polarization and foster invasion of carcinoma cells [40].