Sun Damage Causes Newly Discovered Melanoma-Driving Genetic Changes

Melanoma researchers have been struggling with this question: Which mutations drive this cancer that lead to ultraviolet (UV)-induced genetic damage in tumor cells caused by sunlight exposure?

There have yet to be any mutations conclusively tied to melanoma. The great quantity of these passenger mutations has pulled away from the search for genetic driver mutations that are most important in melanoma development and progression.

Scientists at the Broad Institute of MIT and Harvard, the Dana-Farber Cancer Institute and The University of Texas MD Anderson Cancer Center created a method to mark the drivers while amongst a great amount of passengers. They then found 6 genes with driving mutations in melanoma, three having damage inflicted by UV light which causes recurrent 'hotspot' mutations. The research can be found in the July 20 issue of the journal Cell.

Co-senior author Lynda Chin, M.D., Professor and Chair of MD Anderson's Department of Genomic Medicine, explained:

"Those three mutations are the first 'smoking gun' genomic evidence directly linking damage from UV light to melanoma. Until now, that link has been based on epidemiological evidence and experimental data."

"This study also is exciting because many of the recent large-scale genomic studies have not discovered new cancer genes with recurrent hot-spot mutations, a pattern strongly indicative of biological importance," added Chin, who also is scientific director of MD Anderson's Institute for Applied Cancer Science.

According to the researchers, each of the six new melanoma genes they identified are all significantly mutated and provide possible targets for new treatments.

Thousands of Potential Mutations Recognized, Only Need A Few Dozen Significant Ones

There had previously been a great deal of important mutations recognized as melanoma drivers, but they were falsely identified because the majority of these mutations do not seem to be caused by direct damage from UV light, including:

• BRAF (V600)- present in half of all melanomas
• NRAS (Q61)

Although those known mutations are valuable, there is still missing information. Compared with other types of solid tumors, Melanoma has higher genetic mutation rates. Most are attributable to passenger mutations resulting from damage by UV light, resulting in a DNA alteration called a cytidine (C) to thymidine (T) transition.

Chin, along with Levi A. Garraway M.D., Ph.D., associate professor at Dana-Farber Cancer Institute and Harvard Medical School, and senior associate member at the Broad Institute, used 121 melanoma samples paired with normal DNA and sequenced the exons (active portions of DNA that are involved in protein synthesis). The experts found 86,813 coding mutations. The consequential mutation rate was larger than in any other tumor type reported.

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