Sun worshippers, take heed: Researchers say they have found a connection between multiple basal cell skin cancers—the most common type of skin cancer—and a “significantly increased risk” for later developing a host of unrelated cancer types, including melanoma as well as colorectal cancer, breast cancer, prostate cancer and blood cancer.
People diagnosed with six or more basal cell skin cancers in a 10-year period are three times more likely to develop another cancer compared to people who have never had that type of cancer, according to data from a decade-long study by Stanford University.
Basal cell carcinoma accounts for 80 percent of all skin cancer diagnoses, amounting to about 4 million new cases a year. It’s considered the most benign cancer because it’s slow-growing and is nearly always treated successfully when caught early. Its chief cause? “Repeated and unprotected skin exposure to ultraviolet (UV) rays from sunlight, as well as from man-made sources such as tanning beds,” according to the American Cancer Society. UV rays can damage the DNA of skin cells, interfering with cell growth and division. It should be no surprise then that basal cell carcinomas are most often found on the head or neck, or other parts of the body exposed to the sun, such as the arms and legs.
Stanford’s researchers hypothesized that numerous, frequent basal cell cancers could be a clinical marker of underlying defects in DNA repair. “There’s the belief that there’s damage to mismatch repair genes,” says Anthony Perre, MD, Vice Chief of Staff at our hospital in Philadelphia. “When cells divide, they duplicate the genetic material for the other cell. In the process, some mistakes are made, but part of our genetics is dedicated to fixing these mistakes, and those fixers are called mismatched repair genes. They're supposed to fix the mistake that led to mutations. Having a mutation, or an abnormal change, in mismatched repair genes can put people at risk for a number of different cancers, such as skin, colorectal and others.”
Stanford's initial research involved just 61 patients with “unusually frequent basal cell carcinoma development” over a decade, but the scientists went on to cull data from a medical insurance claims database containing information on more than 250 million U.S. patients. The hypothesis held up.
“We found that about 20 percent of the people with frequent basal cell carcinomas have a mutation in one of the genes responsible for repairing DNA damage, versus about 3 percent of the general population,” said Stanford’s Kavita Sarin, MD, PhD, who characterized the findings as “shockingly high.”
Sarin said the information may help identify those with an increased risk for a separate cancer type before it develops. “Now we can ask patients with repeated basal cell carcinomas whether they have family members with other types of cancers, and perhaps suggest that they consider genetic testing and increased screening,” she said.
Dr. Perre warns that basal cell carcinoma isn’t the only canary in the coal mine, pointing to research published in the Journal of the American Academy of Dermatology that found patients with a history of squamous cell carcinoma are 25 percent more likely to die from a different cancer type. The findings indicate that squamous cell carcinoma “may be a clinical marker of a decline in health.” However, unlike Stanford’s research, the squamous cell study didn’t denote the frequency or number of squamous cell cancers.
Armed with this knowledge, Dr. Perre offers two takeaways: genetic counseling and sunscreen. “If you’re diagnosed with skin cancer, be aware of heredity and possible genetic syndromes,” he says. “Early detection makes a difference. The key is catching and treating it early, which is true of every cancer. Get a skin check at least once a year. All it takes is one blasting sunburn in your life, and the cancer risk increases considerably. And always wear sunblock. It reduces your skin cancer risk considerably.”