The belief that sharks are immune to cancer has circulated widely, leading to questions about their biology and potential secrets for human health. While sharks possess remarkable adaptations, their complete immunity to cancer is a popular misconception. This article explores the origins of this myth and presents the scientific evidence regarding cancer in sharks.
The Myth of Shark Immunity
The belief that sharks do not get cancer gained widespread attention, largely fueled by I. William Lane’s 1992 book, “Sharks Don’t Get Cancer: How Shark Cartilage Could Save Your Life.” This book promoted the idea that shark cartilage contained cancer-fighting elements, a claim further publicized by “60 Minutes” in 1993.
This led to the commercialization of shark cartilage products, marketed as alternative cancer treatments. Despite the marketing, no scientific evidence supports shark cartilage’s effectiveness in treating or preventing cancer in humans. Lane’s company was fined for false advertising, and health organizations caution against using shark cartilage as an alternative to conventional cancer treatments, as it can be harmful.
Do Sharks Get Cancer?
Contrary to the popular myth, scientific evidence clearly shows that sharks do develop cancer. Researchers have documented tumors and cancers in numerous shark species, with the first recorded malignancy in a shark specimen dating back to 1908. Tumors have been found in at least 23 different shark species worldwide.
Documented cases include various types of tumors and cancers affecting different organ systems. For example, a large tumor was observed protruding from the lower jaw of a white shark, and a bronze whaler shark had multiple tumorous lesions on its dorsal surface. These observations demonstrate that sharks are not immune to neoplastic diseases, and even their cartilaginous skeletons, once thought to provide protection, can be affected by tumors.
Cancer might not be observed as frequently in wild animals, including sharks, because sick individuals are often quickly removed from the population through predation or natural processes. Additionally, when sharks die, their bodies typically sink to the ocean floor, making it difficult to detect internal diseases. Despite these challenges, documented cases continue to accumulate, providing further evidence that sharks are susceptible to cancer.
Understanding Shark Biology
While sharks do get cancer, certain biological aspects contribute to a suspected lower incidence compared to other vertebrates. Sharks possess highly efficient immune systems. This robust immune response is believed to play a role in their rapid wound healing and potentially greater resistance to malignancies.
Genomic studies have revealed unique modifications in shark immunity genes, such as legumain and Bag1, which are associated with promoting cancer in humans when overexpressed. In sharks, these genes have undergone evolutionary adaptation, suggesting a modified role that could contribute to their apparent lower cancer rates. Research also indicates that sharks have a very low genetic mutation rate, considered the lowest among all vertebrates. This reduced mutation rate may contribute to a lower likelihood of developing cancer, as mutations can lead to uncontrolled cell growth.
Sharks also have specialized organs, like the epigonal organ, which produces immune cells similar to human bone marrow. Compounds derived from these immune cells have been shown to inhibit the growth of certain human cancer cell lines, while leaving healthy cells unaffected. These biological traits highlight unique adaptations that may contribute to their resilience, but they do not confer complete immunity to cancer.
Lessons from Shark Research
Despite the debunking of the complete immunity myth, legitimate scientific interest exists in shark biology for human health and cancer research. Researchers are actively investigating specific compounds and biological processes found in sharks for their potential therapeutic applications. For instance, squalamine, a steroid found in shark tissues, is being tested for its potential in cancer treatment, as it appears to suppress the formation of new blood vessels that tumors need to grow.
Shark antibodies, particularly a unique type called IgNAR, are also a subject of study. These antibodies are much smaller and more flexible than human antibodies, allowing them to bind to targets in ways human antibodies cannot. Scientists are exploring whether these small antibodies could be used to target cancer cells by inhibiting growth signals.
Beyond cancer, shark research offers insights into other areas of human medicine, such as wound healing and infection resistance. The rapid wound-healing capabilities of sharks are linked to their immune system and genetic adaptations. Understanding these mechanisms and unique proteins could lead to new treatments for various human diseases.