Sharks Get Cancer Too
The claim that sharks hardly ever get cancer does not hold up. Benign and malignant tumours have been documented in sharks and other cartilaginous fish in the scientific literature and the Registry of Tumors in Lower Animals. The actual frequency of cancer in sharks is difficult to determine, however: reports are uncommon and there is no systematic census of all wild animals.
Sharks do have distinctive immune features, including unusual IgNAR antibodies studied in biology and biotechnology. That does not mean sharks are protected from cancer. Shark cartilage and supplements made from it have also not become proven cancer treatments: clinical trials have not demonstrated convincing anticancer benefit, and the FDA has not approved cartilage as a cancer treatment. Laboratory findings about individual molecules do not establish that a dietary supplement treats cancer in people.