The idea that sharks are completely immune to cancer has been a persistent claim in popular culture for decades. This belief suggested that these ancient and successful predators might hold a biological secret to avoiding a major human disease. The evolutionary success of elasmobranchs—the group encompassing sharks, skates, and rays—seemed to lend credibility to this notion.
The Myth Versus Scientific Reality
The widespread conviction that sharks do not develop cancer is fundamentally incorrect, as scientific records confirm these animals are susceptible to the disease. Pathologists have documented various types of tumors, including malignant cancers, in over 40 species of sharks and their close relatives. These tumors have been found in the connective tissues, reproductive organs, and skeletal structures of elasmobranchs.
The myth gained traction in the 1970s and 1980s following research into the anti-angiogenic properties of cartilage. This finding was popularized by a book claiming sharks were virtually cancer-free, leading to the commercialization of shark cartilage supplements. This multimillion-dollar industry marketed powdered shark cartilage as a cancer cure, a claim that lacks reliable scientific evidence or success in human clinical trials. Documented malignancies in sharks date back to the early 1900s, showing the myth stemmed from a commercial misinterpretation of laboratory research.
While sharks do get cancer, the incidence rate may be lower than in many other vertebrates, although the true frequency is difficult to determine due to their inaccessible oceanic environment. The misconception that these animals are cancer-proof has led to the overfishing of certain species, such as the spiny dogfish and hammerhead sharks, to supply the unproven supplement market. The rare observation of tumors in wild sharks may reflect the difficulty in monitoring diseases in deep-sea populations, rather than actual immunity.
Unique Biological Adaptations
Although sharks are not immune to cancer, they possess unique biological mechanisms that may confer resistance or contribute to a lower incidence rate compared to mammals. One studied feature is their skeleton, which is entirely made of cartilage, an avascular tissue that naturally lacks blood vessels.
This led researchers to hypothesize that shark cartilage contains molecules that actively inhibit angiogenesis—the process by which tumors recruit new blood vessels. Anti-angiogenic compounds, such as the small molecule Squalamine and the extract Neovastat (AE-941), have been isolated from shark tissue. While these compounds showed promising anti-tumor activity in laboratory and animal studies, oral consumption of raw shark cartilage supplements has repeatedly failed to demonstrate efficacy in human cancer patients due to poor bioavailability.
Sharks also boast a highly efficient and ancient immune system that may be adept at identifying and eliminating rogue cells. A defining feature is the presence of Immunoglobulin New Antigen Receptor (IgNAR), an antibody found only in cartilaginous fish. Unlike human antibodies, IgNAR is a significantly smaller, single-domain antibody. This small size allows the variable new antigen receptor (VNAR) component of IgNAR to penetrate small crevices and bind to recessed target sites on tumor cells inaccessible to larger human antibodies. Furthermore, the elasmobranch genome shows unique modifications in certain immune and tumor-related genes, such as legumain and Bag1. In humans, overexpression of these genes is associated with cancer promotion, but in sharks, adaptation appears to have modified their function to enhance cellular defense mechanisms.
Recent genomic studies on epaulette sharks suggest they possess the lowest mutation rate among all vertebrates recorded to date. This low rate of genetic change means sharks are less likely to accumulate the DNA damage and mutations that typically initiate the transformation of healthy cells into cancerous ones. This genetic stability, coupled with their unique immune components, contributes to the low observed rates of malignancy.
Implications for Comparative Oncology
The true value of studying sharks lies not in consuming their parts but in borrowing their biological blueprints for human medicine, a field known as comparative oncology. Scientists are focused on translating the unique adaptations of elasmobranchs into novel diagnostic tools and anti-cancer therapies.
The small, stable structure of the shark VNARs is being engineered in laboratories to create highly specific targeting agents. These engineered VNARs can be used to construct new types of targeted therapies, such as Chimeric Antigen Receptor (CAR) T-cell therapy, which could be more effective at penetrating dense solid tumors. Their small size and high affinity also make them ideal for use in nuclear imaging, where they can be attached to radioisotopes to precisely locate and monitor metastatic cancer cells.
Beyond the immune system, the anti-angiogenic factors originally isolated from shark cartilage continue to serve as structural models for pharmaceutical development. Research efforts are focused on creating synthetic drugs based on these natural compounds that maintain their anti-vessel growth properties while ensuring stability and effective delivery within the human body.