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标题: Mythbusting 101: Sharks will cure cancer [打印本页]
作者: StephenW    时间: 2011-9-3 20:32     标题: Mythbusting 101: Sharks will cure cancer

本帖最后由 StephenW 于 2011-9-3 20:35 编辑

                                                                                                        

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                                                                                                                      Mythbusting 101: Sharks will cure cancer                                                                    

Christie Wilcox |                                                                                                                                                                                                                 September 1, 2011 |                                                        
                                                

                                                

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

Tiger Shark at Coconut Island


Sharks are incredible animals. They’re some of the world’s most well known creatures, popular enough to get entire weeks of television dedicated to them. They hold a special place in our hearts and minds. Whether you fear them or love them, or a bit of both, they’ve dominated our oceans for hundreds of millions of years, and still manage to evoke powerful emotions from us.
But, as amazing as they are, they are not going to cure cancer.
First off, there will never be a “cure for cancer”. Not now, not in 50 years, no matter how much we know about how cancers form and spread. And no, it won’t be because there is some big conspiracy, where doctors and pharmaceutical companies are keeping some miracle drug from hitting the market.
You see, there can’t be a cure for cancer, because cancer isn’t a single disease. Cancer is a category of diseases, like rock is a category of music. While rock music is characterized by being song-based, usually with a 4/4 beat and a verse-chorus form, cancer is characterized by cell growth gone terribly wrong, allowing a group of cells to grow uncontrollably. You wouldn’t say that Korn and Elvis sound the same, would you? Well not all cancers are the same, either. Some cancers are slow growing, some are fast. Some are always fatal, others go away on their own.
The thing is, there is no universal trait to all cancers that can be attacked with one treatment, except for the fact that they are cells that grow out of control. Thus a universal cure for cancer would have to be something that prevented and reversed cell growth, which will never, ever be safe to take over an extended period of time. You need cells to grow and replicate in your body – just not when and where they shouldn’t be.
The treatment for a given cancer is heavily dependent on where it is and what it’s doing. There may eventually be a million cures –  a cure for Acute Lymphoblastic Leukemia​, a cure for Basal Cell Carcinoma​, a cure for Craniopharyngioma, and so on and so forth from A to Z – but there will never, ever be a cure for cancer.
But I digress.
The notion that sharks may hold they key to curing cancer rests on the idea that sharks don’t get cancer. Out of all they myths in the world, there are few that have been more ecologically damaging and pervasive despite unequivocal scientific evidence to the contrary. This simply untrue statement has led to the slaughter of millions of sharks via the industry for shark cartilage pills, which are sold to desperate cancer patients under the false pretense that they can help reduce or cure their illness.
The myth started way back in the 1970s when Henry Brem and Judah Folkman from the Johns Hopkins School of Medicine first noted that cartilage prevented the growth of new blood vessels into tissues. This creation of a blood supply, called angiogenesis, is one of the key characteristics of malignant tumors, as the rapidly dividing cells need lots of nutrients to continue growing. It’s not shocking, then, that angiogenesis is a common target for those seeking potential cancer therapies.
Brem and Folkman began studying cartilage to search for anti-angiogenic compounds. They reasoned that since all cartilage lacks blood vessels, it must contain some signaling molecules or enzymes that prevent capillaries from forming. They found that inserting cartilage from baby rabbits alongside tumors in experimental animals completely prevented the tumors from growing1. Further research showed calf cartilage, too, had anti-angiogenic properties2. A young researcher by the name of Robert Langer​ decided to repeat the initial rabbit cartilage experiments, except this time using shark cartilage. Since sharks’ skeletons are entirely composed of cartilage, Langer reasoned that they would be a far more accessible source for potential therapeutics. And indeed, shark cartilage, like calf and rabbit cartilage, inhibited blood vessels from growing toward tumors 3.
Around the same time, a scientist by the name of Carl Luer at Mote Marine Laboratories in Sarasota, FL was looking into sharks and cancer, too. He’d noticed that sharks seem to have relatively low rates of disease, especially cancer, and wanted to test their susceptibility experimentally. So he exposed nurse sharks to high levels of aflatoxin B1, a known carcinogen, and found no evidence that they developed tumors4.
That’s when Dr. I William Lane stepped in. He’d heard about the studies done by Langer and Luer, and become immediately entrenched in the idea that oral shark cartilage could be a treatment for cancer. In 1992 he published the book Sharks Don’t Get Cancer: How Shark Cartilage Could Save Your Life. The book was a best-seller, popular enough to draw in the media from 60 Minutes who did a special on Lane and his new cancer cure. The segment featured Lane and Cuban physicians and patients who had participated in a non-randomized and shoddily done ‘clinical trial’ in Mexico which heralded spectacular results. He then co-authored a second book, Sharks Still Don’t Get Cancer, in 1996.

LaneLabs Shark Cartilage Powder


Of course, Lane started up his own shark fishing and cartilage pill making business called LaneLabs which still makes and sells cartilage pills today. But Lane was not alone – many companies began selling shark cartilage pills and powders as alternative therapies or nutritional supplements. The world market for shark cartilage products was estimated to have exceeded $30 million in 1995, prompting more and more harvesting of sharks for their cartilage.
The results have been devastating. North American populations of sharks have  decreased by up to 80% in the past decade, as cartilage companies harvest up to 200,000 sharks every month in US waters to create their products. One American-owned shark cartilage plant in Costa Rica is estimated to destroy 2.8 million sharks per year5. Sharks are slow growing species, and simply cannot reproduce fast enough to survive such sustained, intense fishing pressure. Unless fishing is dramatically decreased worldwide, a number of species of sharks will go extinct before we even notice.
It’s bad enough that all this ecological devastation is for a pill that doesn’t even work. Shark cartilage does not cure or treat cancer in any way, even in mouse models6. These are also the results of at least three randomized, FDA-approved clinical trials – one in 19987, another in 20058, and a final one presented in 2007 (published in 2010)9. Ingestion of shark cartilage powders or extracts had absolutely no positive effects on cancers that varied in type and severity. To paraphrase Dr. Andrew Vickers, shark cartilage as a cancer cure isn’t untested or unproven, it’s disproven10. Indeed, the Federal Trade Commission stepped in by 2000, fining Lane $1 million as well as banning him from claiming that his supplements, or any shark cartilage derivatives, could prevent, treat or cure cancer.
But what’s worse is that this entire fraudulent enterprise that steals the money of those desperate for any kind of hope is based on a myth. No matter what a money-grubbing man with a PhD in Agricultural Biochemistry and Nutrition tries to tell you, sharks do get cancer.

L: Kidney Tumor, R: Cartilage Tumor


In 2004, Dr Gary Ostrander and his colleagues from the University of Hawaii published a survey of the Registry for Tumors in Lower Animals11. Already in collection, they found 42 tumors in Chondrichthyes species (the class of cartilaginous fish that includes sharks, skates and rays). These included at least 12 malignant tumors and tumors throughout the body. Two sharks had multiple tumors, suggesting they were genetically susceptible or exposed to extremely high levels of carcinogens. There were even tumors found in shark cartilage! Ostrander hoped that this information would finally put to rest the myth that sharks are somehow magically cancer-free.
But it hasn’t. I still see all kinds of shark cartilage pills for sale at the local GNC. But furthermore, the myth that sharks are cancer-free is still believed by many intelligent people.
I read a tweet from The National Aquarium a while ago that said “It must be something in the water. Sharks are the only known species to never suffer from cancer.” The National Aquarium has over 9,000 twitter followers, and this inaccurate tweet was passed on by a number of them, including
The Smithsonian Marine Station in Fort Pierce, FL. How can such a large non-profit, dedicated to “extending the knowledge and resources gained through daily operations toward the betterment of the natural environment” perpetuate such an erroneous and ecologically damaging myth?
Then there’s the BBC, whose division called BBC Earth decided to run a “trick or treat” campaign for Halloween last year featuring truths or falsehoods about different animals. Among them?


When I called them out on their egregious error, they didn’t even admit they were wrong. Instead they simply said that “the science behind their immune systems is still an area of fascination which we know little about, and thankfully people are still studying.”
Maybe I haven’t been clear. Maybe we don’t know everything about shark immune systems, but there is one thing that we do know with 100% certainty.
[size=150%]SHARKS DO GET CANCER.
We can’t even really say they get cancer less often than other species. It’s true that the number of sharks that we have observed with cancer is low. However, only a couple studies have even attempted to look at disease rates in shark species. Furthermore, these studies are hampered by the fact that sharks tend to be wide-ranging, open ocean fish. They live in some of the least contaminated areas on earth. This means that, odds are, they have low levels of exposure to the chemicals that cause cancer in so many land and near-shore species. Furthermore, the odds that a really sick shark would make it into a researcher’s hands to study are slim. A shark whose function is compromised by tumors would likely end up the meal of other, hungry sharks long before they’d end up on a hook cast by scientists. So even the idea that sharks have low rates of cancer or disease is hard to scientifically support.
Perhaps the most disappointing part is that the shark immune system is incredibly fascinating and worth study whether or not it can squash out cancer. Sharks are the earliest evolutionary lineage to have developed an adaptive immune system complete with immunoglobin, T-cell receptors, MHCs and RAG proteins12, and they do it without bone marrow, the source of almost all of our immune system cells. Instead, they have two completely unique immune organs, the Leydig’s and Epigonal organs, that are barely understood. Studying the shark immune system is essential to understanding the evolution of adaptive immunity that is present in all higher vertebrates. And if, indeed, they are resistant to cancer, then that makes the study of their immune system all that much more important.

Carcasses of sharks fished for their fins


Instead, we mindlessly kill millions of them a year to make Asian delicacies and ineffective cancer treatments, and we perpetuate the myth that sharks don’t get cancer. Be assured that whenever I see someone say that sharks don’t get cancer, I will call them out, especially if they should know better. It’s time that this myth is busted once and for all.
Images: A 5′ tiger shark at Coconut Island, photo © Christie Wilcox; LaneLabs Shark Cartilage Powder; Tumor examples from Ostrander et al. 2004. Left: a shark kidney tumor, right: a tumor in shark cartilage; Sharks at a factory finning plant in Japan, photo © Alex Hofford</em>
References

                                                
                                                                                       
                                                                                About the Author: Christie Wilcox is a science writer and blogger who moonlights as a PhD student in Cell and Molecular Biology at the University of Hawaii. Follow on Google+.  Follow on Twitter
@NerdyChristie.
作者: hbv30year    时间: 2011-9-3 22:00

a beautiful and smart author. Now I know cancer is also common in sharks. Cancer is such a horrible and universal disease, it is also an option for the gamblers' game. I hope the gamblers lost all their money in this cruel game.



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