As we age, our risk of developing cancer increases, because our tissue landscape changes as we age.
By Grace Rattue
The study is published in the journalOncogene.
James DeGregori, Ph.D., researcher at the University of Colorado Cancer Center and professor of molecular biology at the University of Colorado School of Medicine, explained: “If you look at Mick Jagger in 1960 compared to Mick Jagger today, it’s obvious that his tissue landscape has changed. And it’s this change, not the accumulation of cancer-causing mutations, that drives cancer rates higher as we grow older.” According to DeGregori, an individual already accumulates a large percentage of the mutations they will have during their lifetime by the time they stop growing in their teens.
He explains: “There’s a mismatch between the mutation curve and the cancer curve, meaning that if cancer were due to reaching a tipping point of say, five or six mutations, we should see higher cancer rates in 20-year-olds, as this is when mutation rate is highest.” Furthermore, healthy tissues are also full of oncogenic mutations. DeGregori says: “These mutations are many times more common than the cancers associated with them.” In other words, more mutations do not mean more cancer. In addition, DeGregori explains that as humans have evolved, our bodies have had to develop new mechanisms to maintain our tissues and avoid disease.
He explains: “But we’re no better at preventing mutations than our yeast or bacteria cousins. You’d think if avoiding mutations was key to avoiding cancer, we’d be better at it than we are.” DeGregori also argues that if these oncogenes were able to take over surrounding tissue, then introducing oncogenes into mice stem cells should help these cells survive instead of hurting them. He continued: “Rather stem cells harboring the oncogenes tend to get weeded out.”
According to DeGregori, the reason the risk of cancer increases with age is because the mechanisms that we have when we are younger to fight cancer deteriorate.
DeGregori said: “It’s like what happened to the dinosaurs 65 million years ago. Dinosaurs were great and they weren’t changing that fast – they were well adapted to their landscape. Until that darn meteor. Suddenly what was fit was no longer fit. The species didn’t have to change their mutation rate – it was the new landscape that drove speciation. Similarly, what primarily drives cancer rates higher as we age is the changed landscape.” The body’s healthy cells function best for healthy, younger tissue conditions. When this balance is changed, for instance, through oncogenic mutation, the cells no longer represent the optimum fit for the surroundings, as healthy cells in young bodies quickly become more successful than cells with cancerous mutations.
He concluded: “When tissue is old, healthy cells are no longer a perfect fit, and mutations might help a cancer cell adapt in ways a healthy cell can’t.”