A series of 105 human melanoma samples was analysed by comparative genomic hybridization for PTEN loss and for the presence or the absence of point mutations affecting NRAS. NRASG183T mutation, resulting in an amino-acid change Q61K, was found in 16 samples (15%), of which 2 also showed homozygous PTEN loss (Supplementary Fig. 5a). Here, PTEN is linked to melanoma.