NEW YORK - In a new study from Denmark, people who had taken aspirin, ibuprofen and related painkillers - especially at high doses and for years at a time - were less likely to get skin cancer, compared to those who rarely used those medications.
The findings add to growing evidence that long-term use of the medications, known as nonsteroidal anti-inflammatory drugs, or NSAIDs, may help protect people against skin cancers, including melanoma, the deadliest type.
Still, research has not been unanimous in that finding: one large 2008 report found no link between NSAIDs and melanoma.
The drugs have also been linked to an increased risk of kidney cancer and come with known bleeding risks -- so more research is needed to weigh the possible harms and benefits of the drugs outside of pain relief, researchers said.
But the lead author on the new study said it would make sense if NSAIDs were tied to skin cancer risk.
"NSAIDs work by inhibiting specific enzymes involved in inflammation," Sigrun Alba Johannesdottir, from Aarhus University Hospital, told Reuters Health in an email.
"Previous studies show that elevated levels of these enzymes are found in skin cancer and that they are involved in important steps of cancer development such as inhibition of cell death, suppression of the immune system, and stimulation of invasiveness and blood vessel growth," she explained.
For the new research, Johannesdottir and her colleagues looked back at records from more than 18,000 people in northern Denmark with skin cancer, both melanoma and less-risky forms of the disease, between 1991 and 2009.
They matched each of those cancer cases with another ten people of the same age and gender without cancer and compared their prescription drug records for the years before the cancer patients were diagnosed.
Thirty-eight per cent of people without cancer had filled more than two prescriptions for an NSAID, according to their medical records.
The researchers found that people with a history of using aspirin and other NSAIDs had a 13 per cent lower risk of melanoma compared to non-NSAID users, and a 15 per cent lower risk of squamous cell carcinoma, another less-deadly form of skin cancer.
There was no difference in the risk of basal cell carcinoma, a third cancer type, based on whether or not Danes had used NSAIDs, according to findings published Tuesday in Cancer.
When the researchers looked specifically at people who had filled prescriptions for the drugs over at least seven years, and used them twice a week or more, they found a stronger link: long-term, high-intensity NSAID users had a 46 per cent lower risk of melanoma, a 35 per cent lower risk of squamous cell carcinoma and a 17 per cent lower chance of getting basal cell carcinoma.
According to the Centers for Disease Control and Prevention, close to 60,000 people in the US were diagnosed with melanoma in 2008, the most recent year with available data, and just under 9,000 died from the disease.
About two million people nationwide are diagnosed with non-melanoma skin cancers each year, but only about 5,000 people die from squamous cell and basal cell carcinomas combined.
Aspirin and other NSAIDs can be bought over-the-counter in the US for a few cents per pill.
The researchers cautioned that there were some limitations to their findings - including that they didn't have information on other possible risks for skin cancer, such as exposure to ultraviolet light, and not all Danish cancer cases were included in their registries.
One dermatologist not involved in the new study said to clarify the link between NSAIDs and skin cancer, a "gold standard" trial is needed - in which people are randomly assigned to take the drugs or not, then followed to see who develops cancer.
"More work needs to be done to examine this association," said Dr. Maryam Asgari, a research scientist at Kaiser Permanente in Oakland.
"I don't think I'd recommend to people, 'Hey, take an aspirin a day to prevent skin cancer,'" she told Reuters Health.
"I don't think we have enough data to say that. I think we do have enough data to say, certain NSAIDs appear to be promising."
Johannesdottir agreed that promoting painkiller use based on these findings isn't warranted.
"Because there are also risks associated with the use of NSAIDs, we cannot give recommendations on NSAID use in general. It is up to the patient and his/her physicians to balance benefits and harms," she said.
And, she added, "The most important prevention against skin cancer remains sun protection."