By Samantha Arrowsmith
The recent publication in January of a new article on metal concentrations in Caribbean Reef sharks is just the latest research paper in a growing field exploring the effect that pollutants are having on sharks. Most are showing some form of contamination and some are leading to questions about whether what we are doing is causing sharks to develop cancer at a higher rate than ever before.
This is a long cry from only thirty years ago when we were emphatically told that sharks could not get the disease at all. So what has brought about this new line of study and what does it say about the past myths and the future possibilities of sharks’ connection with cancer?
Past myths: Sharks can’t get but can cure cancer
It has taken scientists and an army of internet eco-warriors decades to combat a myth that has so much evidence against it that one can only wonder how it ever took hold in the first place.
The answer is a catchy book title, a media savvy presence and a lot of desperate customers.
In 1992 Dr I William Lane published his book, Sharks Don’t Get Cancer: How Shark Cartilage Could Save Your Life which followed up on some early research by scientists Henry Brem, Judah Folkman, Robert Langer and Carl Luer showing that shark and rabbit cartilage have certain properties that can inhibit the growth of the blood vessels that malignant tumours need to grow and spread. Although he admitted within the pages of the book itself that the first part of the title wasn’t exactly accurate, it spawned a natural supplement pill industry that has caused the death of thousands of sharks and offered false hope to thousands of desperate patients. Even today, internet vendors continue to extoll the benefits of their pills, claiming that ingesting cartilage has huge benefits for heart health, anticancer treatments, boosting immunity, combating infertility, improving skin health, reducing radiation sickness, accelerating wound healing, reducing inflammation and improving vaccine effectiveness, something which has become even more pertinent with the arrival of COVID-19.
This has led scientists on a 30 year mission to set the record straight.
Whilst sharks do seem to have some kind of resistance to disease, they are not immune to cancer. Research has shown that they have a comparatively primitive immune system, with high levels of a single immunoglobulin and the ability to release immune cells which can mature as they circulate in the bloodstream. This allows the shark’s body to fight off illness, including cancer, at a much earlier and intense rate than mammals. But this is a far cry from saying that they are immune to it and there is plenty of evidence to prove it.
The first tumour was discovered in the liver cells of a Blue Shark specimen in 1908, and since then cases of cancer have been found in twenty-three species of shark in all parts of their body, including their skin, liver, kidneys, digestive system, mouth, testes and fins. In 1976, a report was published on the discovery of a tumour on a Grey Reef Shark, and in 2004 a Sand Tiger Shark had a cancerous tumour removed. 2004 also saw a comprehensive survey carried out by a team led by Professor Gary Ostrander into the Registry for Tumours in Lower Animals. This found 24 cases of tumours in sharks, two species of which were so susceptible that they had two different types of cancer each. In 2010 a study was conducted on a Nurse Shark with skin cancer, and two of the most recent identifications were located near Australia in 2013 on the jaw of a Great White and the head of a Bronze Whaler Shark. One of the most iconic photographs of a shark was taken on this trip, clearly showing the abnormal growth on the Great White Shark’s jaw.
So, if the scientific evidence shows that sharks are not immune to getting cancer themselves, what is there to show that they can cure it in humans? Well, to be frank, very little.
To begin with, not only do we know that sharks can die of cancer, but several have actually been found to have tumours in their cartilage. So if the wonder substance touted as a cure is actually capable of being targeted by the disease itself, how can pills made of it work? This is something picked up on by Ostrander who reported that ‘scientific evidence to date supports neither the efficiency of crude cartilage extracts nor the ability of effective components to reach and eradicate cancer cells.’
Perhaps what is worse is the pseudoscience that Lane used to found his business empire. Investigations later conducted into the clinical trials he used to prove the effectiveness of his drugs exposed that they had been undertaken without proper controls or medical standards in place. His results were void and lacked any scientific basis. Or, to put in another way, as Dr David Shiffman said in 2013: ‘…eating shark products won’t cure cancer any more than me eating Michael Jordan would make me better at basketball.’
Modern scientific research has not given up on the idea that sharks may hold the key to understanding wound healing and cancer protection, but the work is slow and expensive, and it focuses on genome mapping rather than crude and ineffectual science.
“There’s still tons to be learned from these evolutionary marvels,” marine scientist, Dr Mahmood Shivji said in 2019, “including information that will potentially be useful to fight cancer and age-related diseases, and improve wound-healing treatments in humans, as we uncover how these animals do it.”
But if each new study moves us further away from the old myth that sharks can’t get cancer, do they introduce the new possibility that we just might be giving it to them?
Present realities: are humans giving sharks cancer?
Ongoing research certainly seems to present evidence that sharks are vulnerable to pollution. They are ideal candidates for biomagnification and a 2016 report published in Science of the Total Environment found a considerable build-up of pollution in Blue Sharks, concluding that ‘the impact of contamination…can ultimately lead to the degradation of core ecological aspects, such as swimming, feeding, and reproduction.’ Every region of the planet has been affected in some way, from the nitrogen runoff in Hawaii which has been linked to tumours in sea turtles, to the build-up of carcinogenic petroleum hydrocarbon compounds found in a variety of shark species in the Gulf, including some which were still unborn.
Ostrander also asked questions about the effects of pollution on sharks. His discovery of the two sharks with two different forms of cancer each led him to consider if they had either ‘…a genetic susceptibility to cancer or high carcinogen exposure.’
And then there is the plastic that we throw away; not just the large bags and bottles which, if eaten, cause starvation, but also the microscopic particles that are flushed into our oceans. The plastic soaks up carcinogens from the water before being swallowed and lodged in the stomachs of fish and sharks, particularly bottom and filter feeders. 67% of sampled sharks in a recent 2020 study contained plastic microparticles in their stomachs.
The counter argument is, of course, that the science is just getting better. We are locating more sharks and have better methods of conducting research which is therefore seeing more positive cases. It is hard to refute this when there is a current lack of in-depth studies to give us a baseline for cancer levels in sharks, but the opportunities to study sick sharks is still hampered by the wide, deep waters in which they live, and invasive studies are ethically challenging.
The question therefore is how long we wait for definite proof of a growth in cases? Or do we wait at all? If we already know that pollution is present and being ingested, why don’t we do something now?
Future possibilities: so what are we going to do about it?
Wherever else the solution might lie, it must have one foot in education and, therefore, in research. Dr Christie Wilcox explains that ‘out of all the myths in the world, there are few that have been more ecologically damaging and pervasive despite unequivocal scientific evidence to the contrary.’ Changing the image of sharks and of the way that we use them is essential if we are going to save them.
If we want to see a decrease in the number of sharks and other marine animals with cancerous growths, then we have to clean up our oceans. This means less single-use plastic, a ban on micro-plastics that become carcinogenic when eaten and an embargo on flushing our waste into the sea.
We’ve come a long way from the 1990s when even aquariums were telling their visitors about the amazing way that sharks didn’t get cancer, and we have education to thank for it. More is needed. A ban on shark cartilage pills will help, but ultimately, cartilage pills will only stop being sold online when there is no one left who wants to buy them or no more sharks left to make them from.
Further reading
Alberts, Elizabeth. Sharks are polluted with plastic, new study shows 12 August 2020
Al-Hassan JM, Afzal M, Rao CVN, Fayad S. Petroleum Hydrocarbon Pollution in Sharks in the Arabian Gulf, Kuwait University June 2000
Alves Luís MF, Nunes M, Marchand P, Le Bizec B, Mendes S, Correia J, Lemos M, Novais S. Blue sharks (Prionace glauca) as bioindicators of pollution and health in the Atlantic Ocean: Contamination levels and biochemical stress responses. Science of The Total Environment, Volumes 563–564, 2016, Pages 282-292.
Bernstein, Larry. Demythologizing sharks, cancer, and shark fins. 22 June 2013.
Duke University, Pollution linked to lethal sea turtle tumors 30 September 2014.
Hendricks, Melissa Predators Promise. John Hopkins University Magazine. June 2000.
Marra NJ, Stanhope MJ, Jue NK, Wang M, Sun Q, Pavinski Bitar P, Richards VP, Komissarov A, Rayko M, Kliver S, Stanhope BJ, Winkler C, O’Brien SJ, Antunes A, Jorgensen S, Shivji MS. White shark genome reveals ancient elasmobranch adaptations associated with wound healing and the maintenance of genome stability
Proceedings of the National Academy of Sciences March 2019, 116 (10)
Ostrander GK, Cheng KC, Wolf JC, Wolfe MJ. Shark cartilage, cancer and the growing threat of pseudoscience. Cancer Research, Volume 64, Issue 23. 1 December 2004.
Parton, KJ, Godley, BJ, Santillo, D. et al. Investigating the presence of microplastics in demersal sharks of the North-East Atlantic. Sci Rep 10, 12204 (2020).
Shipley, ON, Lee, CS., Fisher, NS et al. Metal concentrations in coastal sharks from The Bahamas with a focus on the Caribbean Reef shark. Sci Rep 11, 218 (2021).
Smith, Albert C and Hartley, Fount K, Keloid in the Gray Reef Shark, Pacific Science (1976), Vol. 30, No.2, p. 109-112.
Wilcox, Christie. Mythbusting 101: Sharks will cure cancer 1 September 2011.