Basal cell carcinoma is not only the most common form of skin cancer in the United States — it’s the most common cancer overall. Close to a million new cases are diagnosed each year. Luckily, this type of cancer is easily treated and unlikely to spread. It can, however, cause extensive damage to surrounding tissue and bone if it’s not removed.
The biggest risk factor for basal cell carcinoma (BCC), as well as several other types of skin cancer, is sun exposure. People with light skin, hair, and eyes — who have low levels of the protective skin pigment melanin — are at especially increased risk. It’s therefore not surprising that many of the genetic variants associated with skin cancer are also linked to fair pigmentation.
A new study, published online Sunday in Nature Genetics, has identified two SNPs on chromosome 1 that increase the risk of BCC, but are not linked to a person’s coloring.
After studying more than 2,000 people with BCC and close to 36,000 controls from Iceland and Eastern Europe, Stacey et al found that each A at rs7538876 and each G at rs801114 increased the odds of developing BCC 1.28 times over those with two Gs or two Ts, respectively.
(23andMe customers can check their data by clicking on the links above that lead to our Browse Raw Data feature)
The authors of the study estimate that about 1.6% of people with European ancestry have two copies of the riskier versions at both of these SNPs, and that these people have 2.98 times the odds of BCC compared to people who have no risky copies.
The researchers then looked at the DNA of people with two other types of skin cancer that, like BCC, are related to sun. But in about 400 people with squamous cell carcinoma and about 2,000 with cutaneous melanoma, they saw no association with the SNPs.
“One unifying theme may be that genes associated with fair pigmentation confer cross-risk of all three skin cancer types because of their roles in protection from the shared risk factor of UV light, whereas the more specifically associated variants may act through different pathways,” the authors write in their report.
To investigate this idea further, the researchers looked to see if the two new BCC-associated SNPs were related to pigmentation at all. In a sample of about 5,000 Icelandic people they found that neither SNP was linked to eye or hair color, nor were either of them linked to a propensity to freckle or sun sensitivity.
“Taken together, these data suggest that the [SNPs] act through pathways other than those related to UV-susceptible pigmentation traits,” the authors write.