It is the kind of claim that sounds too elegant to be wrong. Sharks, those ancient and seemingly indestructible predators, have swum the oceans for more than 400 million years — long before trees existed, long before dinosaurs. Surely, the story goes, evolution must have equipped them with some special defense against cancer. And if sharks never get cancer, then whatever is inside them must hold the secret to beating the disease in humans, too. Powder it, capsule it, sell it.

You can still find this claim today: in health-food store aisles, in the reviews of shark cartilage supplements on shopping sites, in forwarded messages and wellness blogs. The pitch is seductive because it stitches together three things people want to believe — that nature hides miracle cures, that a fearsome animal must be biologically superior, and that a simple powder can outsmart a disease that has humbled modern medicine. In the 1990s, this story built a global market worth tens of millions of dollars a year and sent industrial fishing fleets after sharks on a scale that helped collapse entire populations.

There is just one problem, and it is not a subtle one. Sharks get cancer. They have been getting cancer for as long as scientists have been looking, and the evidence has been sitting in a public tumor registry for decades. The story of how a catchy book title overpowered that evidence — and how much damage the confusion caused — is one of the clearest case studies ever assembled of pseudoscience outrunning science.

*Illustration: the coastal shallows where many shark species hunt — waters their supposed cancer immunity was said to protect. Image: Unsplash.*

The Claim, As It Circulates

Strip the marketing gloss away and the claim is simple: sharks do not get cancer, so shark cartilage — dried, powdered, and swallowed in capsules — can prevent or cure cancer in people. The supplement bottles promised, in various wordings over the years, immune support, anti-tumor effects, and hope. The logic was presented as common sense. Cartilage contains no blood vessels. Tumors need blood vessels to grow. Therefore shark cartilage must contain something that starves tumors, and eating it must deliver that something to a sick person.

The claim traveled through several distinct channels. There were the books, starting with Sharks Don’t Get Cancer in 1992. There were the supplement brands, most famously BeneFin, sold by Lane Labs-USA. There was credulous television coverage — the Skeptic’s Dictionary notes that the book’s author got “a major news show to do a shoddy, uncritical story which suggested that maybe there was something to the miracle cure.” And then there was the great amplifier of word of mouth: the title itself. Four words, absolute and memorable, repeated so often that the nuance inside the book — to the extent there was any — never stood a chance.

Even reputable institutions have repeated the myth. Scientific American’s David Shiffman, writing a 2014 myth-busting piece, described reading a tweet from the National Aquarium claiming that “sharks are the only known species to never suffer from cancer,” a message then passed along by thousands of followers including the Smithsonian Marine Station. He also described calling out BBC Earth for running the same falsehood in a Halloween “trick or treat” campaign — and getting a shrug in response. When aquariums and the BBC repeat a claim, ordinary consumers can hardly be blamed for believing it.

Where the Myth Came From

The modern version of the myth has a birth certificate: a book published in 1992, Sharks Don’t Get Cancer, by I. William Lane — who held a PhD in agricultural biochemistry and nutrition — and Linda Comac. Lane was not a shark biologist or an oncologist. He was, however, the founder of a company that sold shark cartilage powder, which meant the book and the product were two halves of the same enterprise. The book argued that sharks very rarely develop cancer and that their cartilage could therefore be used against the disease in humans. The title dropped the “very rarely” and went with the absolute.

The timing was perfect. Public fascination with alternative cancer treatments was high, distrust of pharmaceutical companies was a reliable marketing lever, and the 1990s supplement industry was booming under loose regulation. The world market for shark cartilage products was estimated to have exceeded $30 million as early as 1995, according to Scientific American’s reporting. Lane’s promotional machine — books, interviews, infomercial-style marketing — turned a fringe idea into a household belief.

There was, to be fair, a kernel of real science at the bottom of the story, and understanding it explains why the myth was so persuasive. In the 1970s, the surgeon and researcher Judah Folkman pioneered the study of angiogenesis — the process by which tumors recruit new blood vessels to feed themselves. Cartilage is one of the few tissues in the body with no blood supply of its own, and laboratory work showed that cartilage contains substances that inhibit the formation of blood vessels. That is a genuine, interesting finding. The leap from “cartilage contains anti-angiogenic compounds in a petri dish” to “swallowing powdered shark skeleton cures cancer” is where science ended and marketing began. But the kernel of truth gave the claim a veneer of scientific respectability that pure invention could never have achieved.

Sharks Do Get Cancer: The Paper Trail

Here is the part the supplement industry hoped you would never check: scientists had documented cancer in sharks long before anyone claimed they were immune to it. The first tumor ever recorded in a cartilaginous fish — the class Chondrichthyes, which includes sharks, skates, and rays — was found on a skate in 1853. The first tumor found on a shark followed in 1908, in the liver cells of a blue shark specimen. The myth of shark cancer immunity was therefore false for nearly a century and a half before the book that popularized it was even written.

The most thorough demolition came in 2004, when biologist Gary Ostrander and colleagues published a comprehensive survey in the journal Cancer Research. They combed the scientific literature and the U.S. National Cancer Institute’s Registry of Tumors in Lower Animals — a real, public archive of documented animal cancers — and found 42 tumors in sharks and related cartilaginous fishes. These were not ambiguous lumps. At least a dozen were malignant, they appeared throughout the body — skin, liver, kidneys, digestive system, mouth, reproductive organs, fins — and two sharks had two different cancers each, suggesting either genetic susceptibility or heavy carcinogen exposure. Most devastating of all for the myth: several tumors were found growing in shark cartilage itself. The very tissue being sold as a cancer shield was itself vulnerable to the disease.

The case reports make for grim reading precisely because they are so ordinary. In 2004, researchers described a blue shark caught in the northwestern Atlantic with a malignant tumor in its gums — gingival cancer, confirmed under the microscope by prolific abnormal cell growth and chronic inflammation. That same year, a cancerous tumor was removed from a sand tiger shark. In 2010, a nurse shark was documented with skin cancer. And in 2013, off the coast of Australia, researchers photographed one of the most striking cases on record: a great white shark with a large abnormal growth on its jaw, alongside a bronze whaler shark with a tumor on its head. The photographs from that expedition became some of the most widely shared images in shark science — visual proof that the ocean’s most feared predator is not exempt from the disease.

Ostrander’s team drew the obvious conclusion, and they stated it with unusual bluntness for a scientific paper. They acknowledged the possibility that highly purified extracts might one day prove useful, but they criticized promoters for ignoring basic questions of mechanism and toxicity while suggesting that crude cartilage powder could be “curative of all cancers.” And they offered an analogy that deserves to be quoted in full, because it demolishes the central logic of the supplement with a single image: “We know, for example, that there are bacterial proteins that allow other proteins to function in boiling hot environments. Does this mean that we should expect to survive in boiling water after eating crude extracts of those bacteria? Obviously, no.”

That is the entire fallacy in one paragraph. Even if sharks were unusually resistant to cancer — which the registry shows they are not — resistance in the animal would not transfer to a person swallowing its powdered remains. Digestion breaks proteins down. Dose, delivery, and mechanism matter. The supplement’s logic skipped every one of those steps.

*Illustration: shark cartilage was sold with the trappings of medicine, but controlled trials found no benefit against any cancer. Image: Unsplash.*

The Pills Don’t Work — and the Government Said So

Set aside the “sharks don’t get cancer” premise for a moment and ask the narrower question: do the pills do anything? Here the answer is not merely “unproven.” It is tested, replicated, and negative. At least three randomized, controlled clinical trials examined shark cartilage against cancer. A 1998 trial found no benefit. A 2005 trial run by the North Central Cancer Treatment Group — published in the journal Cancer — tested shark cartilage in patients with advanced disease and found it inactive. And a congressionally mandated study completed in 2007, led by Dr. Charles Lu of the M.D. Anderson Cancer Center in Houston, tested a pharmaceutical-grade shark cartilage extract developed by the Canadian company Aeterna Zentaris; the results, published in 2010, again showed no meaningful benefit.

The U.S. National Cancer Institute’s summary of the evidence is unambiguous. In a randomized study of patients with advanced breast or colorectal cancer, shark cartilage did not improve survival or quality of life compared with placebo when both groups also received standard care. In an earlier phase I/II study of 60 people with advanced cancer who took oral shark cartilage, investigators observed no complete or partial tumor responses and concluded the product was inactive under the study conditions. As Scientific American put it, paraphrasing physician and researcher Dr. Andrew Vickers: “shark cartilage as a cancer cure isn’t untested or unproven, it’s disproven.”

The products were not merely useless; they carried real downsides. Documented side effects of shark cartilage supplements include nausea, gastrointestinal upset, and hypercalcemia — abnormally high calcium in the blood, which can be dangerous. Far worse is the opportunity cost. Cancer Research UK, which maintains a page specifically on shark cartilage as an alternative therapy, states plainly: “It was once thought that sharks can’t get cancer. But this is not true. Sharks can get cancer.” The charity warns that using shark cartilage instead of conventional treatment such as chemotherapy or radiotherapy “can be very harmful to your health.” Desperate patients were spending money they could not afford on powder that did not work, sometimes delaying or replacing treatments that did.

Regulators eventually caught up. On June 29, 2000, the U.S. Federal Trade Commission prohibited Lane Labs-USA from claiming that BeneFin “or any other shark cartilage product prevents, treats or cures cancer” without substantial scientific evidence — evidence the company did not have. The order came with a $1 million penalty. The FDA likewise took action against shark cartilage products marketed with unproven anti-cancer claims. The enterprise that began with a book title ended, in the legal sense, with a federal ban on repeating it.

*Illustration: the 2004 survey of the Registry of Tumors in Lower Animals found 42 documented tumors in sharks and their relatives. Image: Unsplash.*

Why the Claim Survived the Evidence

If the evidence is this one-sided, why does the claim persist? Part of the answer is the title’s terrible efficiency. “Sharks don’t get cancer” is four words long, vivid, and easy to repeat. The correction — “a 2004 survey of the Registry of Tumors in Lower Animals documented 42 neoplasms across chondrichthyan species, including at least 12 malignancies and several in cartilage tissue” — is not. In the marketplace of attention, the slogan wins every round.

Part of the answer is the kernel of truth. The anti-angiogenesis research was real, and legitimate pharmaceutical researchers did investigate purified cartilage-derived compounds — Neovastat, the drug tested in the M.D. Anderson trial, was developed as an actual pharmaceutical through proper phase I and II studies, a world apart from powdered supplement capsules. The existence of serious research gave the supplement marketers something genuine to gesture at, even though that research ultimately failed too.

And part of the answer is psychological. The claim flatters a deep human preference: the idea that nature has already solved our hardest problems and hidden the answers in charismatic animals. It is the same impulse behind rhino horn, tiger bone, and bear bile — the belief that consuming a powerful animal transfers its power. Conservationists have a name for the result when that impulse meets industrial marketing: they have called the shark cartilage boom “a triumph of pseudoscience and marketing over scientific evaluation.”

The Verdict

False. Sharks get cancer, and we have known it since 1908.

The evidence against the claim is layered and independent. Tumor registries hold 42 documented cases in sharks and their close relatives, including at least a dozen malignancies and tumors growing in cartilage itself. Individual cases — a blue shark with gum cancer, a great white with a jaw tumor photographed off Australia, a nurse shark with skin cancer — are documented in peer-reviewed literature. The foundational premise of the supplement industry is therefore not a simplification or an exaggeration; it is the opposite of the truth.

The secondary claim — that eating shark cartilage treats cancer in humans — fails on its own terms as well. Multiple randomized trials found no benefit, the National Cancer Institute’s review found no improvement in survival or quality of life, and the FTC fined the leading promoter $1 million and banned the cancer claims outright. The only thing the evidence supports is the kernel the myth grew from: cartilage contains compounds that affect blood vessel formation in laboratory settings, a finding that never translated into a treatment and never implied that sharks were cancer-free.

*Illustration: the claim still circulates in search results and store aisles, decades after the evidence settled the question. Image: Unsplash.*

The Hidden Cost of a Catchy Title

The most sobering part of this story is not that people were fooled — it is what the fooling cost. To feed the supplement market, industrial harvesting of sharks expanded enormously. Scientific American’s reporting described cartilage companies harvesting up to 200,000 sharks every month in U.S. waters, with one American-owned processing plant in Costa Rica estimated to destroy 2.8 million sharks per year. North American shark populations fell by as much as 80 percent over roughly a decade. Sharks are slow-growing animals that reproduce late and bear few young; they cannot withstand that kind of sustained pressure. Species were pushed toward extinction to manufacture pills that did not work, for a disease the animals were never immune to in the first place.

There was a human cost as well, measured in money and in lost time. Cancer patients — often frightened, often facing grim prognoses — paid for hope by the bottle. Some used the powder alongside real treatment, wasting money. Some used it instead, wasting something irreplaceable. The FTC’s $1 million fine, large as it sounds, was a fraction of what the industry extracted from the desperate.

And the myth’s afterlife continues. Shark cartilage products remain for sale in health stores and online marketplaces, their labels now carefully worded to stay inside the law while the old title’s promise lingers in the branding. The book’s four words still surface in casual conversation, in trivia nights, in social media threads. Each repetition is a small tribute to one of the most successful — and most thoroughly debunked — health myths of the modern era.

*Illustration: sharks have swum the oceans for over 400 million years — and shared cancer with the rest of the animal kingdom all along. Image: Unsplash.*

There is a lesson here that extends beyond one supplement and one animal. The shark cartilage story shows how a claim can be wrong in its premise, wrong in its mechanism, disproven in clinical trials, penalized by regulators — and still survive, because it is short, vivid, and tells people what they wish were true. The antidote is not complicated, but it is unglamorous: check the registry. Read the trial. Ask what the evidence actually says, rather than what the title promises. The sharks, it turns out, were never the miracle. The miracle is that anyone checked at all — and that the checking, eventually, won.