People who have had common skin cancers may be at an increased risk of getting cancer again in their life, according to a new study.
The study found that women with nonmelanoma skin cancers (such as basal cell carcinoma or squamous cell carcinoma) were 26 percent more likely to later develop another form of cancer, compared with women who didn't have these skin cancers. In men, the risk increased by 15 percent, the study found.
The study included more than 150,000 people who were followed for more than 20 years, so the findings strongly add to the growing evidence of a link between skin cancer and later development of other cancers, said Anthony Alberg, a professor of epidemiology at the Medical University of South Carolina.
The increased risk of cancer seen in the study isn't high enough to warrant recommending that people with nonmelanoma skin cancers undergo cancer screening tests earlier or more often than generally recommended, said Alberg, who was not involved in the new study. It does, however, raise the question of whether more screening might be beneficial for this group, and future studies might look at this, he said.
Nonmelanoma skin cancers are "so common we can't even count them," so the findings have public health significance, Alberg said. A 2006 study showed there were 2.1 million cases of non-melanoma skin cancer in the U.S.
The link may also help researchers to better understand cancer biology, he said.
The new study is published today (April 23) in the journal PLOS Medicine.
How cancer risk increases
For the study, researchers led by Jiali Han, an associate professor of dermatology at Harvard Medical School, looked at cancers among people participating in two large studies — the Health Professionals Study, which began in 1986, and the Nurses' Health Study, which began in 1984. By 2008, about 29,500 cases of cancer had been diagnosedin the 153,600 people in these studies.
Results showed that people with nonmelanoma skin cancer were at an increased risk of developing the deadly skin cancer melanoma, and that women with nonmelanoma skin cancer were at increased risk of lung cancer and breast cancer, according to the study. The researchers accounted for factors that could affect the results, such as people's ages, smoking, and for women, the use of hormone replacement therapy.
Alberg said that previous studies have linked common skin cancers with an increased risk of other types of cancers. In the new study, there was increased risk of other types of cancer as well, but these increases did not rise to the level of statistical significance. Still, the fact that 23 out of 28 cancer sites examined were trending toward an increased risk means there is likely something underlying the links, he said.
"The increase really doesn't map well with any specific cancer… there's more of a general increase in cancer risk," he said.
Why the link?
The link between nonmelanoma skin cancers and developing melanoma later may be due to sun exposure, the researchers said.
But the reason for the general increased risk of other cancers is unclear. Some researchers suspect that the cellular machinery involved in DNA repair may not work as well in some people, leaving them at an increased risk for any type of cancer, Alberg said.
By studying people who have developed more than one type of cancer, a situation called "multiple primary cancers," researchers can develop a better understanding of cancer biology, he said. The skin cancers in the study are common, and unlike other primary cancers, they are not typically treated with radiation or chemotherapy, both of which have been linked to increased cancer risk later on.
"Looking at these cases, we might really be able to find what causes these risks," Alberg said.
Pass it on: Skin cancers are linked to risks of developing other cancers.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.