Ocean of Pseudoscience: Sharks DO get cancer!

i-cb283a4c5a6df5ada0685195b806f827-pseudoceanweek-thumb-150x149-55471.pngThe sea is a dark and often mysterious place, and it's no wonder that the fear and fascination with the marine world has led to more than a few inaccurate claims. The crew over at Southern Fried Science have decided that this week is all about busting pseudoscience and the myths that surround our ocean realm. As it turns out, I'd posted about one of these before. So here, in honor of Ocean of Pseudoscience week, is a repost busting the myth that sharks don't get cancer.

ResearchBlogging.orgThere 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 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.

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.
1. Brem H, & Folkman J. (1975). Inhibition of tumor angiogenesis mediated by cartilage. J Exp Med (141), 427-439 DOI: 10.1084/jem.141.2.427
2. Langer R, & et al (1976). Isolations of a cartilage factor that inhibits tumor neovascularization. Science (193), 70-72 DOI: 10.1126/science.935859
3. Lee A, & Langer R. (1983). Shark cartilage contains inhibitors of tumor angiogenesis. Science (221), 1185-1187 DOI: 10.1126/science.6193581
4. Luer CA, & Luer WH (1982). Acute and chronic exposure of nurse sharks to aflatoxin B1 Federal Proceedings, 41
5. Camhi M. Costa Rica's Shark Fishery and Cartilage Industry. http://www.flmnh.ufl.edu/fish/Organizations/SSG/sharknews/sn8/shark8new… (1996).
6. Horsman MR, Alsner J, & Overgaard J (1998). The effect of shark cartilage extracts on the growth and metastatic spread of the SCCVII carcinoma. Acta oncologica (Stockholm, Sweden), 37 (5), 441-5 PMID: 9831372
7. Miller DR, Anderson GT, Stark JJ, Granick JL, & Richardson D (1998). Phase I/II trial of the safety and efficacy of shark cartilage in the treatment of advanced cancer. Journal of clinical oncology : official journal of the American Society of Clinical Oncology, 16 (11), 3649-55 PMID: 9817287
8. Loprinzi CL, Levitt R, Barton DL, Sloan JA, Atherton PJ, Smith DJ, Dakhil SR, Moore DF Jr, Krook JE, Rowland KM Jr, Mazurczak MA, Berg AR, Kim GP, & North Central Cancer Treatment Group (2005). Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial. Cancer, 104 (1), 176-82 PMID: 15912493
9. Lu C, Lee JJ, Komaki R, Herbst RS, Feng L, Evans WK, Choy H, Desjardins P, Esparaz BT, Truong MT, Saxman S, Kelaghan J, Bleyer A, & Fisch MJ (2010). Chemoradiotherapy with or without AE-941 in stage III non-small cell lung cancer: a randomized phase III trial. Journal of the National Cancer Institute, 102 (12), 859-65 PMID: 20505152
10. Vickers, A (2004). Alternative cancer cures: "unproven" or "disproven"? CA: A Cancer Journal For Clinicians, 54, 110-118 DOI: 10.3322/canjclin.54.2.110
11. Ostrander GK, Cheng KC, Wolf JC, & Wolfe MJ (2004). Shark cartilage, cancer and the growing threat of pseudoscience. Cancer research, 64 (23), 8485-91 PMID: 15574750
12. Flajnik MF, & Rumfelt LL (2000). The immune system of cartilaginous fish. Curr Top Microbiol Immunol (249), 249-270


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Wow. That's really depressing.

I'm running on anecdote here, but it seems strange to me that many people who are heavily into pseudoscientific 'natural' cures, like shark cartilage pills, are often doing so because of or in association with environmental concerns.

Surely there's some cognitive dissonance there.

Great post, though sad to see that misinformation about sharks and cancer is still being spread about by organizations that should know better. I was particularly shocked by the National Aquarium tweet because, if I recall correctly, at least one of their captive sand tiger sharks was afflicted with cancer in the not too distant past. I heard this from one of the docents on a behind-the-scenes tour there about 15 years ago, and while that is just an anecdote, I can't imagine that the person I had talked to would have lied about it. I wonder if this case ever made it into the literature?

Excellent as always. I missed this the first time around, so thanks for re-posting. Dave will be tackling several shark myths all week long, so don't forget to check out Southern Fried Science for an Ocean of Pseudoscience all week long!

Really useful, thanks! I work for a cancer charity and this question often crops up.

Very informative! One questions: Has there been any fruitful developments from the original studies on the anti-angiogenic properties of cartilage?

Christie, this is a fabulous post, exhaustively referenced, and expertly written!

I've long had an interest in this shark cartilage business because of how it's actually been well-investigated, as dietary supplements go, and, as you note, disproven.

You reminded me of an old post about Salmonella contamination of shark cartilage supplements in 2007 that I just repurposed in my new home.

And Lee, I did also write somewhere about clinical trials with AE-941 (Neovastat) but will have to dig that up.

If only the Darwinian solution helped, as in: people getting fatal diseases die of them when treating them informed by superstition. Unfortunately, there are so many people easily convinced by magical thinking that they will out-reproduce any other species.
Extrapolating, it is logical that the single-species planet is a question of when, not if, since we can be certain that the incentive to make a profit by inventing more miracle treatments using ever more pulverized species is far more powerful than the conscientious decision to not risk the collapse of entire ecosystems.
Hopefully the sane and rational segment of Earth's population can stand in their way and put an end to this mania of "like-cures-like", "opposite-cures-like", "natural-cures-anything", "dilution-is-power", "if-it-looks-like-a-penis-it-will-help-my-penis", etc..

The inclusion of "Pseudoscience" in the title is generous at best given that this doctor simply jumped on what he saw as a profitable enterprise without allowing peer reviewed research to find a conclusion. In doing so, he became yet another snake oil salesman who not only potentially risks the lives of patients by offering them an ineffective alternative to current cancer treatments, but has also caused such devastating environmental damage to shark populations by his actions.

Unfortunately, I have seen shark blood and shark cartilage pills being advertised by far too many web pages.

I had no idea that people thought that sharks don't get cancer, or the fanciful notion that we can cure our own by slaughtering them. Our rape of the oceans is truly tragic.

"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?"

Oh dear. The implications of that statement are enormous. In fact it calls into question all institutions that fail to provide sources for their statements. I can distinctly remember an argument at the Smithsonian that was rebutted with an all-knowing âThe guide told me so!â

Excellent references by the way...

By Apothecary (not verified) on 06 Sep 2010 #permalink

I find it bizarre that, even if it were true that they don't get cancer, that somehow grinding them up into pills would magically give people their cancer-resistance!

very interesting and well researched blog. you deserve success with this work and i hope it helps spread the word.

Christy -- it's not totally absurd. The idea is that something in the cartilage is preventing angiogenesis (the point of many chemotherapeutic agents), so getting that substance in your blood ought to do the same to the tumor. A sort of all-natural chemo. The problem, of course, is that whatever the substance is, it's not likely to survive the gut, so simply eating lots of shark cartilage probably isn't going to help you. Also, you'll need to get a high serum concentration of it in order for it to be useful, even if it can be absorbed, and that's going to mean doing more than just taking a few pills. You might need to eat half a shark's skeleton to do it.

That was the essential problem with Pacific Yew as a chemotherapeutic agent. It has a substance in its bark which can treat breast cancer -- and unlike shark cartilage, it really does work. You can even get it orally. But you'd have to eat an enormous amount of bark to get enough of it in your blood -- in which case you might not have to worry about breast cancer because you're too busy dying of a bowel obstruction. So you could extract it from the treebark and then concentrate it, right? Well, turns out you'd have to basically strip the Olympic Peninsula bare. So researchers worked out another way to get the chemical, and today it is marketed as Taxol.

It's never as easy as the shark cartilage salesmen want us to think.

By Calli Arcale (not verified) on 08 Sep 2010 #permalink

Thanks for that Christie. Nicely done!

By Jeff Campbell (not verified) on 09 Sep 2010 #permalink

I applaud the principle of your post - its bogus that sharks don't get cancer and the cartilage cure is bunk - but there's a couple of statements in your post that aren't quite right.

The first: "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". Thatâs not even close to true. Fish health folks have been looking at sharks for diseases and parasites as long as they've looked at other fishes. Some, like Janine Caira, have systematically surveyed sharks and rays all over the world for their pathogens, while others have made piecemeal contributions that nonetheless add up to a sizeable body of literature. Indeed, your own citation of the Ostrander review of RTLA submissions later in the post tends to counteract your statement. I did a quick check on CAB Abstracts and the search string "(elasmobranch* or shark*) and (parasit* or disease*)" gets over 600 hits.

Secondly: "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". You seem to be framing sharks as the "Jaws"-type of open ocean carcharhinids or lamnids, and framing cancer as something caused by pollution. Neither is accurate. Many sharks, perhaps the majority, are coastal and associated with the bottom, like bamboo sharks, wobbegongs, nurse sharks, dogfish and so on. They are just as exposed to contaminated coastal water and sediment as bony fishes. Its also important that cancer isnât always caused by contaminants â thereâs all sorts of genetic and spontaneous neoplasias as well.

Thirdly: "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." In principle this could be true, but you're assuming that the tumors are always debilitating, which is probably rarely the case, and it would be a bear of a hypothesis to test. Also, extending this logic we would never find cancer in bony fishes either, and thatâs certainly not so. Cancers of many kinds, including both pollutant-caused and spontaneous kinds, are far from uncommon throughout the diversity of fishes.

There's little doubt that sharks DO get get cancer, but equally little doubt that they get LESS cancer than bony fishes or mammals, and exactly why that is is not yet clear. It doesn't change your main gist about the cartilage cures, but it would be a shame to replace that bit of scientific misinformation with another bit.


First off, parasites are very different from cancer. I check Jaine's papers, and none deal with cancer or overall disease rates - they all are new or interesting species of parasites specific to a single host, which is an entirely different field (though totally cool). She has not looked at cancer or other disease rates in different groups of sharks, as far as I can tell. As for pelagic versus reef fish - very few, even something like a black tip, are truly highly coastally associated, in particular the ones that are caught for cartilage cures. My point is that tigers, sandbars or the other large sharks that are often caught (wobbegongs hardly make the high catch list) are not as coastal or reef-dwelling as we assume.

The fact is, until there is a systematic study of disease in sharks, we don't know what disease rates are, and we can't claim they do or don't have any diseases less or more than other species.


Your first quote said "cancer OR ANY OTHER DISEASES", so to discriminate parasites after the fact is somewhat disingenuous. Even setting aside parasites, you didn't address the fact that there are hundreds of papers about the diseases of sharks, many of which are about cancers. You can't simply say there are no studies, or even no "systematic" studies, because neither is true. To insist that it is does a disservice to those who study shark health for our profession, and those who came before. Check out, for some examples:
Stoskopf, M. K. 1993. Clinical pathology of sharks, skates and rays. In: Fish Medicine, p. 754-757. M. K. Stoskopf (ed.). W. B. Saunders Company, Philadelphia, Pennsylvania, USA.

Horsley, R. W.; A review of the bacterial flora of teleosts and elasmobranchs, including methods for its analysis. Journal of Fish Biology, 1977, 10, 6, pp 529-553, 95 ref.

Pereira, N. M.; Peleteiro, M. C.; Osteoma in the skin of a tawny nurse shark, Nebrius ferrugineus (Lesson). Journal of Fish Diseases, 2002, 25, 9, pp 565-567, 8 ref.

Borucinska JD, Frasca S. 2002. Naturally occurring lesions and micro-organisms in two species of free-living sharks: the spiny dogfish, Squalus acanthias L., and the smooth dogfish, Mustelus canis (Mitchill), from the north-western Atlantic JOURNAL OF FISH DISEASES 25:287-298

Mylniczenko ND, Harris B, Wilborn RE. 2007. Blood culture results from healthy captive and free-ranging Elasmobranchs. JOURNAL OF AQUATIC ANIMAL HEALTH 19: 159-167

Borucinska, J. D.; Harshbarger, J. C.; Bogicevic, T.; Hepatic cholangiocarcinoma and testicular mesothelioma in a wild-caught blue shark, Prionace glauca (L.). Journal of Fish Diseases, 2003, 26, 1, pp 43-49, 40 ref.

Borucinska, J. D.; Harshbarger, J. C.; Reimschuessel, R.; Bogicevic, T.; Gingival neoplasms in a captive sand tiger shark, Carcharias taurus (Rafinesque), and a wild-caught blue shark, Prionace glauca (L.). Journal of Fish Diseases, 2004, 27, 3, pp 185-191, 37 ref.

Your second argument, about the distribution of sharks, is just incorrect. Look at the distribution of the species you mentioned. Two are entirely coastal and one is predominantly coastal:
Blacktips http://www.flmnh.ufl.edu/fish/gallery/descript/blacktip/blacktipmap.JPG
Sandbars: http://www.flmnh.ufl.edu/fish/gallery/descript/sandbarshark/pl.mapcopy…
Tigers: http://www.flmnh.ufl.edu/fish/gallery/descript/TigerShark/cumap.JPG , which is predominantly coastal.

I am sorry if I appear argumentative, but this series about debunking pseudoscience should be held to as high or even higher standard of rigor than any other scientific blog post, simply by its topic.


I think you misunderstand what I mean by "systematic". I'm not arguing that no one has looked at a disease in a shark - Ostrander's paper is case and point, showing that a number of tumors have been found in sharks. But to look at disease rates in a large population, you have to sample a decent number of that population and inspect them for diseases. "Naturally occurring lesions and micro-organisms in two species of free-living sharks: the spiny dogfish, Squalus acanthias L., and the smooth dogfish, Mustelus canis (Mitchill), from the north-western Atlantic " does do this, but it's limited in sample size and that it's temporally and locationally restricted. Twenty or so samples from Long Island Sound is not a systematic investigation of Squalus acanthis, considering its population ranges from the southern Pacific to northern Atlantic with limited population genetic structure, suggesting that these fish regularly migrate and interbreed on an almost global scale. I'm not saying such a systemic investigation is easy - indeed, it's expensive, time consuming and overall challenging, hence why it hasn't been done.

Publications which describe diseases that have been found do not fall under this, unless they specifically sampled the larger population at random and took frequency data of disease presence. This has not been done for the vast majority of shark species. Show one study that compares the rates of a given disease (parasites, cancer, etc) in more than a few species of elasmobranch, and I'll agree that it's been compared through the genera and that there are higher or lower rates in sharks than other animals. But I haven't seen that paper, and none of the ones you have provided fit that category.

Thank you for writing about this! What an important issue. It reminds me of the kind of stuff I often see at http://www.youtube.com/greenopolistv and it's always great to be educated and kept up to date on what's going on!

I was talking with someone else about the oil in the ocean. Never really thought about Sharks and for that matter any other species being able to get cancer...

Below was some of the thins we had posted.

"(the amount of oil pouring into the water is now thought to be closer to 20,000 barrels a day rather than the 5,000 barrels that BP has insisted on for weeks.)"

You can always guarantee that the estimate is undervalued when it come to any catastrophic accident. Unfortunately that's the way our government thinks. They insist on lying to the people even though they know we don't believe it. They do it anyways just because they can.

"Benzene is probably the best known of these compounds, because it's been flagged as a human carcinogen for a couple decades."

Yeah just imagine the amounts of that material that is now in the gulf. BP says naaawww your gulf is clean now... LOLOL most of the oil is resting on the sea floor because of the chemicals used to "CLEAN IT UP". Just think about all the food we eat out of the gulf. I can't wait to see the long term health effects that this will present to us. :(