“Although promotions of bogus cancer 'cures' have always been a problem, the Internet has provided a mechanism for them to flourish,” said Margaret O'K. Glavin, the FDA's associate commissioner for regulatory affairs. “These warning letters are an important step to ensure that consumers do not become the victim of false 'cures' that may cause greater harm to their health.”

The companies were hawking products made with ingredients as varied as bloodroot, Cat's Claw, and shark cartilage, and touting them as magic elixirs for treating everything from melanoma to bladder cancer. Some companies went so far as to claim their products caused "cancer cells to disappear," "malignant tumors to shrink," and could "target cancer cells while leaving healthy cells alone."

The FDA says these products are not approved to prevent or treat cancer because they have not been shown to be safe or effective for this purpose. Some of these products are even harmful.

The crackdown was spurred by consumer complaints, which then led to an investigation conducted by the FDA, Federal Trade Commission, and members of the Mexico-United States-Canada Health Fraud Working Group. The warning letters, which are also posted on the FDA's Web site, threaten seizure of the illegal products, injunction, and possible criminal prosecution should the companies fail to correct their violations.

Earlier this year, the FDA sent 112 similar warnings to Web-based companies who were falsely promoting cancer treatments.

For more information on this topic, see our guide to Complementary and Alternative Therapies.