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Sharks and Cancer

Do sharks get cancer?

Yes, but cancer occurance in sharks and rays is very rare.

Wait, I thought they didn't get cancer?!?

Actually, sharks can and do get cancer. According to the Smithsonian's Registry of Tumors in Lower Animals, there have been around 42 shark tissue samples found that are suspected to be tumorous. Most of these samples however are fibrous responses to wounds, parasites, or goiters (enlarged thyroid glands) and are not malignant. Sharks and rays do seem to have a lower incidence of disease than other animals.

If sharks really can get cancer, then why do people take shark cartilage pills as a cancer remedy ?

The claim that shark cartilage pills can help cure cancer was based off of research done by Massachusetts Institue of Technology and Mote Marine Laboratory. The results of the research showed only that a very small amount of an active material, with limited ability to control blood vessel growth, can be obtained from large amounts of raw cartilage. There was never any claim by the researchers, however, that freeze-dried shark cartilage pills could "seek out" a malignant tumor in a cancer patient and inhibit the blood vessels feeding it, because such a claim is not logical. Crushed shark cartilage pills have never proved to be of any use as a cure against cancer.

What does the cartilage have that could block cancer and cause people to think shark cartilage pills would work?

Tumors release chemicals stimulating the capillary growth so a nutrient-rich blood supply is created to feed the tumorous cells. This process is called angiogenesis. If scientists can control angiogenesis, they could limit tumor growth. Cartilage has a noticable lack of capillaries running through it. Early research into the anti-angiogenesis properties of cartilage revealed that tiny amounts of proteins could be extracted from cartilage, and, when applied in concentration to animal tumors, the formation of capillaries and the spread of tumors was inhibited. Unfortunately for humans, the tiny amount of anti-angiogenesis materials in a ground cartilge pill would be destroyed during digestion of the pill.

Well, if it doesn't hurt people, who cares if someone wants to take shark cartilage pills?

Sharks are being threatened on all sides. Hunted for their fins to supply the shark fin soup market and slaughtered for their reputation as dangerous man-eaters, shark populations around the world cannot afford another strain from people seeking a large source of cartilage for pills. Sharks grow and mature slowly, meaning it takes them a long time to reproduce. When sharks do reproduce, it is usually in small numbers. Millions of sharks are slaughtered for a "cure" that does not work.

In addition to being an ineffective cure, shark cartilage pills might also harm people. People could have allergies to shark cartilage, or too much shark cartilage might be toxic to humans. More reliable research must be done to evaluate the potential risks from shark cartilage pills.

 

Also, many researchers feel that selling shark cartilage pills as a cure for cancer is morally wrong because it does not work. Fighting cancer is a long, painful, and expensive process and selling cancer patients a pill that has not shown any curative abilities at all is unethical.

Okay, so if sharks get cancer and cartilage pills don't work, why is Mote Marine Laboratory still interested in shark cancer research?

Mote Marine Laboratory recognizes that despite the failure of shark cartilage pills as a treatment for cancer, sharks remain a valuable research animal for studying the development of cancer treatments. Sharks do show a lowered frequency of disease, inlcuding tumors, and researchers at Mote are studying the shark's unique immune system to unlock the secrets of shark health.

For more information on Mote's research with sharks and cancer:

  • Read a Mote Magazine article on a new breakthrough for cancer research found by Mote scientists
  • Find out about the National Cancer Institute grant that helped fund cancer research at Mote

So, sharks get cancer, cartilage pills don't work, Mote focuses on research other than cartilage pills...is there still any research on the cartilage pills out there?

Yes. New products containing shark cartilage extracts are currently being tested for their antiangiogenesis properties. These products are showing potential for cancer treatment, but some of them are still in test trials only. Dosage amounts and potential side effects of the treatments are being studied.

 

Further readings: Rivlin, M.A. 2000. "Bad to the Bone" The Amicus Journal. 22: 12-18.