

Why don't all whales have cancer? - alexwg
http://icb.oxfordjournals.org/cgi/content/full/icm062v1

======
stcredzero
Related: As a means to fight cancer, large mammals have mechanisms to suppress
telomerase and the other (alt) telomere repair mechanism. Small mammals like
mice do not have this. Why? It wouldn't help them. Even if the cancer cells in
a tumor could not lengthen their telomeres, many of them would still get big
enough to kill the host. (An inch-wide tumor might be no big deal for us, but
for a little field mouse, it's as big as the whole body!) Hence, there is no
evolutionary benefit to these mechanisms, and small mammals do not have them.

It could be that whales do get cancer, but since it's much harder
proportionately for cancer to kill them as compared to merely large mammals
like us, the cancer often goes undetected, and something else kills the whale.
After all, finding 1 inch tumors in a whale would be like finding a needle in
a haystack.

Cancer cells mutate rather rapidly, to the extent that this often impairs
their function. If a cancer doesn't achieve and maintain efficient metastatis,
it won't keep spreading. Perhaps whales have enough bulk that they can simply
absorb being riddled with tumors in what constitutes a small fraction of their
bulk, allowing them to ride the cancer out until it mutates itself past the
point of efficient spread and survival.

~~~
DavidSJ
_Some_ of the descendant cancer cells might lose their capacity for spreading
and survival, but wouldn't selection favor those that maintain it? Is there
really any reason to believe that its reproduction fidelity is so low that
there wouldn't be enough non-mutated cells in each generation?

~~~
stcredzero
"spreading and survival" are contextual. "Cheater" cells might out-compete
other tumor cells locally, but at the cost of the cancer surviving long term
and successfully spreading elsewhere.

------
jldugger
So basically, the theory is that once you get big enough, your tumors
themselves get tumors?

~~~
byrneseyeview
Perhaps the reason whales are the largest mammals is that, for anything
larger, their tumor-tumor get tumors, killing the tumor-tumor and allowing the
tumor to kill the whale.

~~~
GrandMasterBirt
it is very counter-intuitive... but then again evolution is.

whales don't get larger because they need to eat more. whales may be perfectly
sized for their food supply. A theory.

In any case I am about at my limits of my understanding of biology :P

------
gurtwo
What about bigger creatures, like dinosaurs? Is there any evidence of cancer
among them? (I'm totally profane on the subject, just wondering).

~~~
albertcardona
Most (nearly all) dinosaurs were smaller than current whales.

To get a first hand impression, please visit the Museum of Natural History in
New York City, which has many skeletons of both in display.

------
rsheridan6
Why wouldn't the hypertumor go on to kill the host after it killed the tumor?

~~~
jsonscripter
Maybe the hypertumor gets it's own tumor after a while, and the cycle
continues. Or the immune system of the whale which doesn't react to the
original tumor does react to the hypertumor. Or maybe the hypertumor only
grows on the original tumors type of tissue. Etc.

This article is just about a hypothesis. It's anyones guess at the moment.

------
thras
I was just discussing this exact topic with a geneticist friend of mine about
15 minutes ago. Small world.

One thing it does prove is that the problem of cancer suppression has been
solved before. By evolution. That should give researchers a bit of hope at
least.

Edit: He happens to think the linked hypothesis in the article is "bullshit."

~~~
pj
Well, whales live under the water and most mammals have fur, so perhaps they
are protected from the cancer causing sun more than humans. Elephants have
thick protective skin.

Plus, humans tend to be closer to carcinogens like pesticides than other
animals. Those deer in scandanavia are also herbivores...

It seems like they aren't limiting their variables enough. If they really
wanted to determine the correlation between size and cancer, they'd need to
use different sizes of the same species. What is the control group?

~~~
seldo
The sun is _a_ cause of cancer, but not the only or even a primary cause. The
real "cause" of cancer is cell mutation, which can be triggered by sun,
chemical exposure, or simply sheer random chance -- part of the thesis of this
article is that, since whales have so many more cells, the "random chance"
type would be more likely to happen. And one tumor is enough to kill us, so
why not whales? That's the question they're asking.

------
zackattack
Maybe it also gives hope for a new cancer therapy: induce tumors on tumors.
Similar to radiation therapy, except indirect.

------
andybak
Sup Dawg, We heard you like tumors so we...

No?

I'll get my coat.

