According to the increased expression of the Gch1 gene, BH4 and total biopterins concentration were increased in 4C11− and 4C11+ melanoma cells when compared to melanocytes (Figure 2A,D), showing that in the tumor, as demonstrated in other cells, GTPCH1 activity and BH4 production are regulated at the transcriptional level. Here, GCH1 is linked to neoplasm.