PTEN and melanoma: The two most common and studied events are activating mutations in the oncogene NRAS (15–20%) [16–18], and loss of expression or function of the tumor suppressor PTEN (11–60%) [16, 19, 20–24], but mutations of PI3K [25, 26] and AKT3 [27], the predominant AKT isoform in melanoma [28], have also been described.