When our DNA is damaged and cannot be repaired, the damaged cell is marked for termination so its compromised DNA isn't passed on. The cells are told not to reproduce. If this process, called apoptosis, or "programmed cell death," doesn't work—says a newly published paper—then cancer steps in to remove the rogue cells before their broken DNA can be copied and passed on to future generations. It sounds like a sci-fi movie plot, only the result is cancer, not a dystopian future. This effect may also be the reason cancer is so hard to cure.
The study, published in Biotechnology & Biotechnological Equipment, characterizes cancer as a kind of apoptosis designed to protect the integrity of the species, where you or I are killed off to remove our mutated or damaged DNA from the gene pool.
"In the light of the theory that cancer is the final checkpoint," write the authors, "or the [sic] nature’s manner to prevent complex organisms from living forever at the expense of genetic stagnation, the eventual failure of modern anti-cancer treatments is only to be expected."
Thus cancer may be, like growing old and dying instead of living forever, a mechanism to keep our DNA fresh and clean, and our best hope may not be a cure but just better and better tools for slowing down and suppressing cancer enough that we can continue to live normally, without it spreading and killing us.
"Dividing cells have to be able to pass at least four crucially important checkpoints during different phases of the cell cycle," says the study—some, but not all, of which check for DNA damage. One of these is the called the G1/A checkpoint, and one of its tasks is to stop cells with DNA problems. But, like a TSA screener checking for guns in carry-on-bags, it doesn't catch everything. In the short term, say authors Rumena Petkova and Stoyan Chakarov, these lapses do nothing, but in the long term they may multiply and end up becoming tumors.
It's important to note that Petkova and Chakarov's theory is just that, but it's certainly an interesting one. The paper has a section titled "The Tremendous Cost of Living for Ever," which looks at the problems with a race of immortals. The world would fill up pretty quick, for one thing, but genetically, beings that live for ever would be a disaster. The high-fidelity cell-reproduction needed to keep our bodies renewing themselves perfectly without aging would preclude the mutations that drive evolution. Genetic diversity would also decrease, so that if (or rather when) the environment changed, we couldn't adapt, and the whole species would die off.
The theory of cancer being a genetic last-ditch safety mechanism has at least one big counter-argument, though. Most cancer manifests in older people, simply because the longer we live, the more chance we have for something to go wrong. And if a cancer comes along to do it's clean-up after we've passed reproductive age, then it's too late to stop your defective genes from being passed along. Not that gene heredity is that cut and dried, but, like the theory presented here, it's an interesting thought experiment.
The study's conclusion though, is just plain depressing. "A universal and radical solution to the problem of cancer is unlikely to be developed in the near future," it says. Thanks a lot, science.
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