UVB Rays Linked to Milder Skin Cancer
UVA May Be More Important Than UVB for Melanoma -- Best Bet to Avoid Both
Dec. 20, 2005 -- Scientists now say sunlight in the form of UVB rays isn't the main culprit in melanoma.
Melanoma is the deadliest form of skin cancer. Getting a lot of sun early in life is linked to melanoma. It's also linked to nonmelanoma skin cancers such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).
As one gets more and more UVB exposure over time, one's risk of BCC and SCC goes up. That isn't true for melanoma. Now researchers may know why.
Researchers, including Qingyi Wei, MD, PhD, at the University of Texas M.D. Anderson Cancer Center, find that UVB causes a lot of mutations in the basal and squamous cells near the skin surface. The more mutations, the higher a person's risk of cancer.
But UVB doesn't cause many mutations in melanocytes -- the skin cells that can become melanomas.
"Nonmelanoma patients develop tumors quickly once they get enough sunlight," Wei tells WebMD. "But melanoma is tricky. There is not a straight relationship between melanoma and sunlight dose."
BCC and SCC Cancer Patients Sensitive to UVB
What's going on? Wei's team got blood cells from 469 white patients with melanoma, BCC, and SCC. They also looked at blood cells from 329 cancer-free volunteers. They exposed the blood cells to UVB radiation.
Reporting in the Dec. 21 issue of the Journal of the National Cancer Institute, Wei and colleagues report that the UVB rays caused many mutations in the cells from the patients with nonmelanoma skin cancer. That didn't happen in the cells from people without cancer -- or in the cells from melanoma patients.
This, Wei says, means that cells near the skin surface either die or develop cancer mutations as soon as they soak up enough UVB rays. But while melanocytes may pick up a few mutations, they remain alive -- and only later become cancerous.
"Melanocytes do not die easily. They hang in there," Wei says. "They only need the intermittent, intermediate sun exposure when you are a teenager, and then they hang in there and develop into cancer when you're much older. So that means there is something else there, not just sun exposure, causing melanoma."
UVA: The Bad Guy?
Part of that "something else" may be UVA sunlight. UVA rays penetrate deeper into the skin the UVB rays.
"People argue that UVA does play more of a role in melanoma for two reasons," Wei says. "One is that the ozone layer is depleted, so UVA radiation comes down more easily. The second is that early sunscreen products worked against UVB and UVC but not UVA. Later on they developed better ones. But that misled people to feel safer wearing the older products, so they got more exposure to UVA."