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If you were to walk into any health and nutrition store (or internet site) today, you would most likely find bottles of shark cartilage pills. Advertised as having numerous curative powers, including cancer fighting agents, shark cartilage is ingested based on the commonly held belief that sharks do not get cancer. This is yet another shark myth. Just like humans, sharks do get cancer and the number of documented cases of shark cancer is growing.
For the past 100 years, scientists have studied cancerous tumors in sharks. The first chondrichthyes’ (cartilaginous fishes, including sharks) tumor was found on a skate and recorded by Dislonghamcps in 1853 (3). The first shark tumor was recorded in 1908. Scientists have since discovered benign and cancerous tumors in 18 of the 1,168 species of sharks (3). Scarcity of studies on shark physiology has perhaps allowed this myth to be accepted as fact for so many years.
In April 2000, John Harshbarger and Gary Ostrander countered this shark myth with a presentation on 40 benign and cancerous tumors known to be found in sharks (4). In June of that same year, Borucinska, Harshbarger, and Bogicevic (2003), biopsied the body an adult male blue shark, Prionace glauca. The accidentally caught blue shark was found with cancerous tumors in both its liver and testes (3). Several years later a cancerous gingival tumor was removed from the mouth of a captive sand tiger shark, Carcharias Taurus (5). Advances in shark research continue to produce studies on types of cancer found in various species of shark (3,4,5).
Like humans and other vertebrates, sharks seem to contract tumors in response to environmental toxins and pollutants. Piscine hepatic neoplasms, tumors affecting the livers of fishes, are known to plague fish, including sharks, dwelling in polluted waters. Unlike smaller fish, sharks biomagnify pollutants, which may actually make them more susceptible to tumorous growth (3). Much like humans respond to foreign bodies such as asbestos, sharks also seem to develop tumors in response to foreign bodies. For example, the blue shark found in June 2000, was found with a fish hook embedded in its side, possibly resulting in liver cancer (3). It seems that sharks are not nearly as invincible as they were once thought to be.
Unfortunately myths and misconceptions such as these have led to the decimation of many shark species. Despite recorded cases of shark cancer (3,4) and evidence that shark cartilage has no curative powers against cancer (1,2, 4), sharks continue to be harvested for their cartilage.
References:
- Sharks: Cancer fighters? (February 20, 1998). Current Science, 85(11), p. 6.
- Professionals wary of shark cartilage cures (1993). Nutrition Health Review: The Consumer’s Medical Journal, 66, p. 8.
- Borucinska, J.D., Harshbarger, J.C., & Bogicevic, T. (2003). Hepatic cholangiocarcinoma and testicular mesothelioma in wild-caught blue shark, Prionace glauca (L.). Journal of Fish Diseases, 26 (1), 43-49.
- Sharks do get cancer; Cartilage claims in doubt (June 2000). Environmental Nutrition, 23 (6), p. 8.
- Borucinska, J.D., Harshbarger, J.C., Reimschuessel, R., & Bogicevic, T. (2004). Gingival neoplasms in a captive sand tiger shark, Carcharias taurus (Rafinesque), and a wild caught blue shark, Prionace glauca (L.). Journal of Fish Disease, 27, 185-191.
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