cancer in higher animals

 

Cancer is a scary and mysterious thing. In the way of trying to understand it in medical field  to get better at killing cancer , we discovered a biological paradox   Large animals seem to be immune to cancer. The bigger a being, the more cancer it should have .To understand why we first need to take a look at the nature of cancer itself. Our cells are protein structure  made out of hundreds of millions of parts. Which runs only through by chemical reactions, they create and destroy structures,to  sustain a metabolism and  gain energy, and also make almost  perfect copies of themselves (cell division) .these process is called complex chemical reactions pathways. They are biochemical networks upon networks, intertwined and stacked on top of each other. Most of them can barely be involes  by a single human mind and yet they functioned perfectly. Until  they don't. With billions of trillions of reactions happening in thousands of networks over many years, The question is not if something will go wrong, but when.Tiny mistakes add up until the grandiose machinery gets corrupted. To prevent this from getting out of hand, our cells have kill switches that make them commit suicide. But these kill switches are not infallible. If they fail, a cell can turn into a cancer cell. Most of them are killed by the immune system very quickly.  But if immune system fails given enough time a cell would accrue enough mistakes, slipped by unnoticed and begin making more of itself. all animals have to deal with this problem .In general the cells of different animals are the same size. The cells of a mouse aren't smaller than humans. It just has fewer cells in total and a shorter lifespan .Fewer cells and a short life means a lower chance of things going wrong or cells mutating, or at least it should mean that. Humans live about 50 times longer and have 30,000 times more cells than mice, yet the rate of cancer is basically the same in humans and in mice. Even waiter, blue whales with about 3,000 times more cells than humans don't seem to get cancer at all really.This is PETO'S PARADOX  The baffling realization that large animals have much much less cancer than they should. Scientists think there are two main ways of knowing the paradox  evolution and hyper tumors.

·         evolve or become a blob of cancer. As multicellular beings developed a 600 million years ago, animals became bigger and bigger .Which added more and more cells and hence more and more chances that cells could be corrupted .So the collective had to invest in better and better cancer defenses. The ones that did not died out.But cancer doesn't just happen. It's a process that involves many individual cells mistakes and mutations in several specific genes within the same cell .These genes are called proto-oncogenes and when they mutate it's bad news For example with the right mutation,a cell will lose its ability to kill itself.Another mutation and it will develop the ability to hide. Another and it will send out calls for resources. Another one and it will multiply quickly. These oncogenes have an antagonist though;  tumor suppressor genes. They prevent these critical mutations from happening or order the cell to kill itself if they decide it's beyond repair. It turns out that large animals have an increased number of them. Because of this, elephant cells require more mutations than mice cells to develop a tumor They are not immune but more resilient. This adaption probably

·         Hypertumors : hyperparasites the parasites of parasites (parasite that kills the parasite). Hypertumors are the tumors of tumors. Cancer can be thought of as a breakdown in cooperation. Normally, cells work together to form structures like organs, tissue or elements of the immune system. But cancer cells are selfish and only work for their own short-term benefit. If they're successful, they form tumors; huge cancer collectives that can be very hard to kill. Making a tumor is hard work though. Millions or billions of cancer cells multiply rapidly, which requires a lot of resources and energy. The amount of nutrients they can take from the body becomes the limiting factor for growth So the tumor cells stimulates  the body to build new blood vessels directly to the tumor, to feed the cancer cells which  killing the body . And here, the nature of cancer cells may become their own undoing. Cancer cells are inherently unstable and so they can continue to mutate. Some of them faster than their other cancer cells . If they do this for a while,  at some point one of the copies of the copies of the original cancer cell, might suddenly think of itself as an individual again and stop cooperating with other cancer cells . Which means just like the body, the original tumor suddenly becomes an enemy, fighting for the same scarce nutrients and resources. So the newly mutated cells can create a hypertumor. Instead of helping, they cut off the blood supply to their tumors , which will starve and kill the original cancer cells. Cancer is killing cancer. this process can repeat over and over, and this may prevent cancer from becoming a problem for a large organism. It is possible that large animals have more of these hyper tumors than we realize, they might just not become big enough to notice Which makes sense a two gram tumor is 10% of a mouse's body weight, while It's less than 0.002% of a human and 0.000002% of a blue whale. All three tumors require the same number of cell divisions and have the same number of cells. So an old blue whale might be filled with tiny cancers and just not harmed by it . There are other proposed solutions to Peto's paradox,such as different metabolic rates or different cellular architecture.

 

 

 

 But right now we just don't know. scientists are working on the problem. Figuring out how large animals are so resilient to one of the most deadly diseases we know, could open the path to new therapies and treatments. Cancer has always been a challenge.

-Ramnath P