ACTA2 and melanoma: However, to rule out the possibility that the increased expression of ECM genes in TCGA MITFlow melanoma tumors was derived from fibroblast cells, we removed the 130 melanoma TCGA samples that showed the highest expression of the fibroblast markers PDGFRB and ACTA2 and then assessed the expression of collagens across the 30 MITF highest and lowest melanoma samples, which consistently showed that expression of genes encoding ECM proteins are strongly enriched in MITFlow tumors (Figure 3i).