for National Geographic News
Sharks have survived some 400 million years on Earth. Could their longevity be due in part to an extraordinary resistance to cancer and other diseases? If so, humans might someday benefit from the shark's secretsbut leading researchers caution that today's popular shark cartilage "cancer cures" aren't part of the solution.
Carl Luer of the MOTE Marine Laboratory's Center for Shark Research in Sarasota, Florida, has been studying sharks' cancer resistance for some 25 years. He believes that MOTE research (in cooperation with institutions like Clemson University, The University of South Florida, and Tampa's H. Lee Moffitt Cancer Center) might someday lead to help for humans who suffer from cancer.
"Sharks have a low incidence of disease," he said, "but unfortunately many of the observations leading to this conclusion are anecdotal. It's been based on several things. One is that historically, going back to the late 1800s, sharks have been fished commercially and there have been few reports of anything out of the ordinary when removing internal organs or preparing meat for the marketplace.
"Scientists have also been dissecting sharks for years," he continued, "because many of the basic systems that humans have are found in sharks in simpler form. Most pre-medical students who took comparative anatomy probably dissected dogfish sharks, but you don't see reports of cancerous tumors."
Luer says that sharks aren't entirely cancer-free, a mistaken perception that has gained some public acceptance. "Lots of the media will overstate this [resistance] and say, 'sharks don't get cancer.' That's not the case, but their incidence is impressively low, the number of documented cases is low. We don't say that they don't get it, but we think that they must have some way to combat it."
But not all scientists are sure that sharks are even resistant to cancer. Gary Ostrander, professor of biology and comparative medicine at Johns Hopkins University in Baltimore, Maryland, says that just because not a lot of evidence exists doesn't mean that the animals aren't getting cancer.
"We don't know that they don't get cancer," he said. "Any suggestion that they get it at a lower rate than humans or other fish, is prematurebecause there haven't been any carefully conducted systematic studies.
"I have not seen anything in the scientific literature that gives any confidence, with certainty, that sharks get cancer at a lower rate than fish or other species," he said.
The incidence of shark disease is tough to ascertain. Systematic surveys of sharks are difficult to conduct, as capturing the animals in large numbers is time-consuming, and cancer tests would likely require the deaths of large numbers of sharks.
Still, Ostrander says that research like Luer's at MOTE is a positive step into understanding the relationship between sharks and disease.
"Carl and others are asking very good questions," he said. "There may be fundamental differences in shark immune systems so that they aren't as prone to cancer, or so that certain types of compounds might not be a problem for them."
Immune System Could Hold the Key
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