Stop the presses! Sharks do get cancer. This normally wouldn't qualify as big medical news, and I barely noticed the item when it appeared not long ago in the New York Daily News. But think of the huge amount of mythology-and business-that has mushroomed out of a single, easy-to-grasp and, as it happens, false anecdote. If sharks are immune to cancer, wishful thinking went, they must make a protein or molecule that prevents cancer from developing. From this appealing little fiction emerged a thriving branch of alternative medicine: the use of shark cartilage to treat cancer.

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