HGF and metastatic melanoma: To validate the importance of PTEN in melanoma progression in situ, we established conditional PTEN loss in the context of the hepatocyte growth factor/scatter factor (HGF) autochthonous melanoma GEM model, in which a single initiating neonatal dose of UV radiation causes premalignant melanocytic lesions (nevi) by 2–3 months, some of which then progress over the next 6 to 12 months to invasive, metastatic melanoma.34