PTEN and melanoma: The phosphatase and TENsin homolog (PTEN) enzyme converts phosphatidylinositol 3,4,5-triphosphate (PIP3) into phosphatidylinositol 4,5-biphosphate (PIP2), antagonizing the phosphoinositide 3-kinase (PI3K) function and thus suppressing the activation of the PI3K/AKT pathway; functional inactivation of PTEN by deletion or mutation occurs in 30–60% of sporadic melanomas [23].