Naked mole rats never get cancer
newscientist.com
newscientist.com
A mouse weighs 20 grams. I weigh somewhere around 100kg. So I consist of approximately 5000 times more cells than a mouse does.
The longest-lived mouse in recorded history [1] lived just over 5 years. Most mice die of old age in a couple of years. The oldest humans live to be over 100. Thus, my cell lines will undergo somewhere between 20 and 50 more cell divisions than a cell in a living mouse. [2]
What this means is that human cells have to be much better designed to resist cancer than mouse cells. If humans were no more cancer-resistant than mice we'd all be getting cancer as infants. And evolution hasn't bothered to design mice that will resist cancer for fifty years, because no mouse has ever had a chance to live to be fifty.
So while many of the basic facts of cancer are similar in mice and in humans, eventually the details are bound to diverge. This is an uncomfortable fact for researchers.
This also means that, while it's great for the mole rats that they don't get cancer, that doesn't mean they're somehow more immune to cancer than the average human. Even though mole rats are legendary for their longevity -- they can live into their twenties [3] -- the average human has to be less cancer-prone than a mole rat just to get through puberty without needing chemotherapy.
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[1] Google: "Methuselah Mouse Prize"
[2] This is a really simplistic calculation: Among other things, we're neglecting the fact that mice have a rather different metabolic rate from humans, and that different kinds of cells divide at different rates.
[3] Metabolism again: One reason that mole rats are thought to live so long is that they have very slow metabolic rates. Which probably also affects their susceptibility to cancer.
Just curious - is cell division time period same for humans and mice?
Naively, doesn't this imply that elephants and whales are more immune to cancer than the average human?
Another fun fact, whalers find tumor scars in whale bodies all the time, but the whales never seem to die of cancer. The probable answer: whales are just too big to care. If I get a tumor the size of a walnut, I might be able to live with it. For a mouse, that would be a disaster. If I get a tumor the size of my head, that's probably game over. But for a whale, it's no big deal. But a mouse, a whale, and a human all have about the same sized cells. So to be fatal, a whale's cancer cells would have to divide a lot more times. Unfortunately, cancer cells experience a lot more mutations than normal ones. Whales are big enough to be able to afford to let the tumors mutate themselves to death.
But it's not just that the whales are too big to care. In fact, according to published results from folks like the late Judah Folkman, human bodies are also full of little microtumors. The older you get, the more of them there are.
Current theory is that microtumors are forming all the time, but most will remain dormant forever. Only if one of them manages to "flip the angiogenic switch" -- undergo a mutation which makes it able to summon new blood vessels to itself -- will that tumor manage to grow to a size larger than a few hundred microns in diameter. And even then it might not be that big a deal. I guess whales can shrug them off at even bigger sizes than we can.
The problem is when the cancer learns to metastasize. In the immortal (paraphrased) words of cancer researcher Josh Fidler, "if you have a big primary tumor we know what to do: The surgeon cuts it out and off you go." It's not the primary tumor that kills you. It's the metastases that kill you. I bet whalers don't find whales full of metastatic tumors. Unless they're already washed up on a beach.
http://www.eurekalert.org/pub_releases/2009-05/chb-wdp051809...
"The Naked Mole-Rat: A New Long-Living Model for Human Aging Research" http://biomed.gerontologyjournals.org/cgi/content/full/60/11...
"Researchers have found that subterranean mole rats have developed cellular mechanisms in order to survive the low levels of oxygen in their underground habitat -- mechanisms that are similar to those used by tumors to survive and progress in humans."