There are a lot of myths out there about the marine world, but by far the one that bothers me the most is the notion that sharks don't get cancer. 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 tumors3.

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 with 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.

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 compared to other fish, 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 20079. 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.

Even if we hadn't found cancer in sharks, it's highly unlikely that they alone are cancer-free. It's far more likely, instead, that the perceived 'low rates of cancer' are due to the fact that there has yet to be even one study which looked at the rates of disease in sharks. No one has systematically checked these animals for cancer or any other diseases. Even if such a study occurred and did find low rates, it doesn't mean they're even close to immune to cancer. Sharks are pelagic 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 such a 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 researchers.

But 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's cartilage! Ostrander hoped that this information would finally put to rest the myth that sharks are somehow magically cancer-free.

Yet here we are, five years later, and 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. Just ask writer Shelly Silverstone, who tweeted just this week about how sharks don't get cancer. But even worse, just today I read a tweet from The National Aquarium that said "It must be something in the water. Sharks are the only known species to never suffer from cancer." The National Aquarium has almost 4,000 twitter followers, and this inaccurate tweet was passed on by a number of these including The Smithsonian Marine Station in Fort Pierce, FL. A random, misinformed writer I can understand, but 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?

In case I haven't been clear, let me say it again: Sharks do get cancer! There isn't even any evidence to say that they don't get cancer very often, as no one has systematically looked at cancer rates in them. So any statement that even suggests that sharks are cancer resistant is misleading at best, and down right wrong at worst.

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. But instead, we mindlessly kill over 100 million of them a year to make Asian delicacies and ineffective cancer treatments, and we keep brainwashing our kids into believing that shark's don't get cancer. Where are Adam and Jamie when you need them? It's time that the myth of cancer-free sharks is busted once and for all.

References
1. Brem H, Folkman J. Inhibition of tumor angiogenesis mediated by cartilage. J Exp Med. 141, 427–439 (1975).
2. Langer R et al. Isolations of a cartilage factor that inhibits tumor neovascularization. Science 193, 70-72 (1976).
3. Lee A&Langer R. Shark cartilage contains inhibitors of tumor angiogenesis. Science 221, 1185-1187 (1983).
4. Luer CA&Luer WH. Acute and chronic exposure of nurse sharks to aflatoxin B1. Fed Proc 41, 925 (1982).
5. Camhi M. Costa Rica's Shark Fishery and Cartilage Industry. http://www.flmnh.ufl.edu/fish/Organizations/SSG/sharknews/sn8/shark8news... (1996)
6. Horsman MR, Alsner J, Overgaard J. The Effect of shark cartilage extracts on the growth and metastatic spread of the SCCVII carcinoma. Acta Oncologica 37, 441-445 (1998)
7. Miller DR et al. Phase I/II trial of the safety and efficacy of shark cartilage in the treatment of advanced cancer. J. Clin. Oncol 16, 3649-3655 (1998).
8. Loprinzi, C.L. et al. Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial. Cancer 104, 176-182 (2005)
9. Lu, C et al. A phase III study of AE-941 with induction chemotherapy (IC) and concomitant chemoradiotherapy (CRT) for stage III non-small cell lung cancer (NSCLC). J Clin Onco, 25 7527: ASCO Annual Meeting Proceedings (2007)
10. Vickers A. Alternative cancer cures: "unproven" or "disproven"? CA Cancer J Clin 54, 110-8 (2004)
11. Ostrander GK et al. Shark cartilage, cancer and the growing threat of pseudoscience. Cancer Res 64, 8485-8491 (2004)
12. Flajnik MF&Rumfelt LL. The immune system of cartilaginous fish. Curr Top Microbiol Immunol 248, 249–270 (2000).