Why are only some cells 'competent' to form cancer?

Medical researchers report that melanoma formation depends on something called 'oncogenic competence,' which is the result of a collaboration between the DNA mutations in a cell and the particular set of genes that are turned on in that cell. Cells that are competent to form melanoma are able to access a set of genes that normally are closed off to mature melanocytes (the cells that make melanin and give skin its color). In order to access these locked-up genes, the cells require specific protei...