Melanoma – the deadliest and most aggressive form of skin cancer – has long been linked to time spent in the sun. Now a team led by scientists from the Broad Institute and Dana-Farber Cancer Institute has sequenced the whole genomes of 25 metastatic melanoma tumors, confirming the role of chronic sun exposure and revealing new genetic changes important in tumor formation.
As expected, the scientists detected known BRAF and NRAS mutations in 24 of the 25 tumors. Both genes are involved in sending signals important in cell growth.
One other gene leaped out: PREX2, previously implicated in breast cancer for blocking a tumor-suppressor pathway, was altered in 44 percent of patients. In a larger validation cohort of 107 tumors, the frequency of the mutation was 14 percent.
PREX2 is mutated in a convergence of genetic disruption that appears to accelerate tumor development. Its mutations occurred not just at hot spots that typically turn on an oncogene, a type of cancer-causing gene, and drive cancer forward. The alterations were also scattered across the length of the gene in a pattern typically seen when another type of cancer-causing gene, known as tumor suppressors, are turned off.