NGF and melanoma: Furthermore, when we varied the concentration of NGF in co-culture assays, we discovered increasing concentrations of NGF led to a higher percentage of Mart-1:GFP-positive melanoma cells; 500 ng/ml versus 50 ng/ml of NGF doubled the percentage of Mart-1-positive melanoma cells from 3.4±1.5% (s.d.)to 10.3±4.03% (s.d.)(P<0.05; Fig. 2H).