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CancerQuest > Introduction to Cancer Biology > Introduction to Cancer in Animals > Introduction to Cancer in Wild Animals > Shark Cartilage and Cancer: Overview

Shark Cartilage and Cancer: Overview

 

Shark cartilage has been used by many patients to complement traditional cancer treatments.   The effectiveness of the treatments is unclear.  Shark cartilage has not been approved by the FDA for the treatment of any disease, but it is available in the form of dietary supplements.⁽¹⁾ The use of shark cartilage in cancer treatment is based on the mistaken belief that sharks don't get cancer.  An extension of this belief is that shark body parts (i.e. cartilage) can prevent or treat cancer in humans.  However, benign and cancerous tumors can in fact develop in sharks; George Washington University Medical Center researchers reported over thirty tumors found in elasmobranchs, a group of animals that includes sharks, rays, and skates.⁽²⁾ The belief that sharks do not get cancer is not based on the known facts.

Another question that has been posed is whether or not sharks have reduced amounts of cancer.  This is a difficult question to answer because data concerning cancer rates in wild animals (including sharks) are limited, and the information that is available isn't conclusive.  There are some data which suggest that sharks may have a reduced occurrence of cancer.⁽³⁾  Some people interpret this to mean that sharks have some form of resistance to the development of cancer.  If sharks do have lower cancer rates, the reasons are not understood.

Why Cartilage?

The choice of cartilage, instead of some other body part is not random.  The first reason is the availability of the product.  The entire endoskeleton of sharks is composed of cartilage, amounting to about six percent of their body weight.⁽⁴⁾The amount of cartilage that can be obtained from a large shark is therefore quite large.  The second reason is based on some proven biology.  Cartilage, in both sharks and humans, lacks blood vessels.  It has been suggested that sharks resist cancer because of something in their cartilage that inhibits blood vessel growth (angiogenesis).  Angiogenesis inhibitors have been found in the cartilage of other animals.⁽⁵⁾

Growing tumors require angiogenesis to bring them oxygen, sugar and other nutrients.  Without a blood supply, tumors cannot grow beyond a very small size.  Blood vessels also serve as a "highway" for cancer cells to move to distant parts of the body (metastasize).  Angiogenesis inhibitors from other sources are already used to treat cancer patients.  If they exist, it is possible that the angiogenesis inhibitors in shark cartilage could be used create a drug to combat cancer in humans.  

Shark Cartilage and Cancer Cells in the Laboratory

Human studies with shark cartilage have been disappointing. Animal studies have provided some evidence to support its anti-angiogenic activity.  In one study, 0.6 grams cartilage/kilogram of body weight was administered to rats for 4.5 days.  Angiogenesis was then induced in the abdomen of the animals with chemicals.  The animals continued to receive the cartilage treatment for two weeks.  The results showed a notable decrease in blood vessel formation in the rats that had been fed shark cartilage compared with those that were not.⁽⁶⁾In another study, cancer cells were implanted into the corneas of rabbits.  A pellet of highly purified shark cartilage was placed next to the cancer cells.  After twenty days the tumors near to the cartilage showed reduced blood vessel development with zones of complete inhibition around the pellets themselves.⁽⁷⁾

Shark Cartilage and Human Cancer

Because of the results of shark cartilage in animals, several studies were performed in the late 1990's to examine the effectiveness of shark cartilage in treating cancer patients.  The results were disappointing.  In one study, twenty prostate or breast cancer patients received 1 gram/kg/day of an oral shark cartilage powder for twenty weeks.  Both survival times and quality of life were unchanged compared with a placebo control group.⁽⁸⁾   In another study, shark collagen was orally administered to sixty patients with different advanced cancers for six weeks.  The study noted no complete or partial responses.  The outcomes were similar to patients who had received only supportive care.⁽⁹⁾   Clinical trials with a shark cartilage extract, Neovastat® (AE-941), in patients with renal or lung cancer showed only limited or no benefit to patients.^{(10) (11)}

In summary, in model organisms, shark cartilage results in inhibited blood vessel growth.  However, when shark cartilage extracts are administered to cancer patients no conclusive results have been obtained to support the use of shark cartilage as a cancer treatment.

References for this page:

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2. Harshbarger JC. 1999 (pers. comm.). Registry of Tumors in Lower Animals. Department of Pathology, George Washington University Medical Center, Washington, D.C. [http://www.vin.com/Proceedings/Proceedings.plx?CID=IAAAM1999&Category=&PID=49514&O=Generic]
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6. Davis PF, He Y, Furneaux RH, et al.: Inhibition of angiogenesis by oral ingestion of powdered shark cartilage in a rat model. Microvasc Res 54 (2): 178-82, 1997. [PUBMED]
7. Lee, Anne, and Robert Langer. "Shark Cartilage Contains Inhibitors of Tumor Angiogenesis." Science 221 (Sep. 16 1983): 1185-187. [PUBMED]
8. Leitner SP, Rothkopf MM, Haverstick L, et al.: Two phase II studies of oral dry shark cartilage powder (SCP) with either metastatic breast or prostate cancer refractory to standard treatment. [Abstract] Proceedings of the American Society of Clinical Oncology 17: A-240, 1998. [http://www.asco.org/ASCOv2/Meetings/Abstracts?&vmview=abst_detail_view&confID=31&abstractID=12633]
9. Miller DR, Anderson GT, Stark JJ, et al.: Phase I/II trial of the safety and efficacy of shark cartilage in the treatment of advanced cancer. J Clin Oncol 16 (11): 3649-55, 1998. [PUBMED]
10. Lu C, Lee JJ, Komaki R, 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) (NCI T99-0046, RTOG 02-70, MDA 99-303). [Abstract] J Clin Oncol 25 (Suppl 18): A-7527, 391s, 2007. [http://www.asco.org/ASCOv2/Meetings/Abstracts?&vmview=abst_detail_view&confID=34&abstractID=31161]
11. Escudier B, Choueiri TK, Oudard S, et al.: Prognostic factors of metastatic renal cell carcinoma after failure of immunotherapy: new paradigm from a large phase III trial with shark cartilage extract AE 941. J Urol 178 (5): 1901-5, 2007. [PUBMED]