New findings have challenged long-held beliefs about cancer and aging.
A study, conducted on mice by Stanford Medicine researchers, found that the elderly seem to be at a lower risk for the disease, with older rodents developing fewer and less aggressive lung tumors than their younger counterparts over a period of 15 weeks.
The findings fly in the face of the belief that the risk for developing cancer increases with age — though the researchers are still working to understand the biological cause underpinning their results.
But the discovery fits with what doctors have observed in people over 85, an age when the incidence rate starts to drop.
“It’s a striking finding,” associate professor of genetics and of pathology Dr. Monte Winslow, said in a statement.
“We would expect that older animals would get more and worse cancers, but that’s not at all what the study found,” he added. “So, what is it about the molecular changes associated with aging that suppress cancer?”
Comparing dozens of mice that were between four and six months old to mice that were nearly two years old – the average lifespan of a lab mouse is about two years – the team found that the amount of cancer in the younger mice was triple that of the older mice.
They also had larger tumors, former graduate student Dr. Emily Shuldiner explained. “In every way we could measure, the younger animals had worse cancers,” she said.
To better understand what could be causing these differences, the researchers then tested the effect of disabling 25 genes that act to suppress tumors.
One stood out from the rest, known as PTEN.
“PTEN inactivation stood out as having a much stronger effect in young mice,” Shuldiner said. “It suggests that the effect of any given mutation, or the efficacy of cancer therapies targeted at specific mutations, might be different in young versus old people.”
What this could mean for humans remains to be seen. Around 226,650 new lung cancer cases and 124,730 deaths are expected in the U.S. this year, according to the American Cancer Society.
Rates of lung and other types of cancer are rising in younger adults, including people who have never smoked. Changes in screening practices are commonly cited for the rise, as well as gut microbes and indications that some forms can behave differently in those ages groups.
Although humans and mice are incredibly different in many ways, they do share genetic similarities and all humans have the PTEN gene.
A PTEN mutation in humans can cause the formation of benign tumor-like growths called hamartomas that leave people at an increased risk of developing cancer, according to the Cleveland Clinic.
The authors said further research needs to be done into how age can impact tumor growth to update current models used by scientists and potentially develop enhanced treatments for patients.
“The implications of this story could be huge,” biology professor Dr. Dmtri Petrov said. “Maybe aging has a beneficial side to it that we could harness for better therapies.”
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