Why Turtles Might Hold Secrets To Extraordinary Cancer Resistance

NOTTINGHAM, England — While humans agonize over cancer screenings and medical breakthroughs, turtles have been quietly living their best lives for more than 250 million years — and they get cancer at astonishingly low rates. New research suggests these ancient reptiles might offer clues to why some animals seem almost immune to one of nature’s most devastating diseases.

A new study published in BioScience reveals that turtles develop cancer at exceptionally low rates compared to many other vertebrate groups studied. After analyzing hundreds of turtle necropsies (animal autopsies) from zoos across Europe, the UK, and the United States, scientists found cancer rates so low they make even the healthiest human populations look cancer-prone by comparison.

What makes these findings so striking is something scientists call Peto’s paradox: the puzzling observation that larger, long-lived animals should theoretically develop more cancer because they have more cells that could potentially turn malignant over time. Turtles seem to defy this expectation.

Galapagos giant tortoises, for example, can live well over 150 years and weigh more than 300 kilograms (about 660 pounds), giving them far more cells and far more time for cellular problems to arise compared to smaller, shorter-lived animals. Yet these ancient giants rarely develop tumors.

Cancer Rates That Defy Logic

The research team — including scientists from universities in Birmingham, Nottingham, and multiple zoos across Europe and the U.S. — compiled necropsy data from 290 turtles representing 64 different species. This spanned eight zoos and included everything from tiny 150-gram leaf turtles to massive Galapagos tortoises.

Among all 290 turtles examined, researchers found only one case of neoplasia — the scientific term for any abnormal tissue growth — and no malignancies, meaning no cancerous growths that spread aggressively. This translates to neoplasia prevalence estimates of 0.34% and cancer prevalence estimates of 0% for this study.

For comparison, mammals typically show mean cancer prevalence values around 10%, while birds average about 3%. Even other cold-blooded reptiles like squadmates (a group that includes snakes and lizards) show about 7% cancer prevalence. These numbers are still dramatically higher than what researchers see in turtles.

Previous research backs this up too. A century-long analysis of 511 necropsies at the Philadelphia Zoo (1901–2002) found six cases of neoplasia, with four confirmed cancers. In all, neoplasia and cancer prevalence show estimates of about 1.2% and 0.78%, respectively. Even when cancer did occur, it rarely metastasized (spread to other parts of the body), unlike many human cancers.

Built-In Biological Defenses

So, how do turtles pull this off? Scientists think these animals have evolved sophisticated biological defenses. Genomic analyses of large, long-lived species like Galapagos and Aldabra giant tortoises have revealed positive selection and duplications (extra copies) of important tumor suppressor genes, along with genes that regulate metabolism, the immune system, and the maintenance of their DNA. Essentially, they’ve evolved genetic “backup systems” to detect and eliminate potentially dangerous cells.

Comparative studies also show that Galapagos tortoises express higher levels of proteins that help control cell growth and handle stress inside the cell. For example, their cells are unusually good at triggering apoptosis — a kind of cellular self-destruct program — to deal with endoplasmic reticulum (ER) stress, which can otherwise lead to cancer if damaged cells survive.

Turtles also live life in the slow lane: their metabolic rates are about 5–10% lower than mammals of similar size. This slower pace reduces the production of reactive oxygen species — chemically reactive molecules that can damage DNA over time and contribute to cancer.

They’ve even evolved ways to withstand extreme conditions that would damage or kill most other animals. Some turtles can survive freeze-and-thaw cycles, go without oxygen for extended periods, and upregulate antioxidant defenses in the brain. All these tricks help protect their cells from damage that would otherwise build up with age.

Missing Pieces and Future Research

Despite these fascinating clues, scientists still have gaps to fill. Most available data comes from zoo animals, which likely live longer than wild turtles, giving more time for cancer to appear as an age-related disease — but wild populations are largely unstudied in this context.

Certain turtle groups, like side-necked turtles (Pleurodira) and softshell turtles (Trionychidae), remain especially underrepresented in necropsy samples. And apart from research on virus-driven tumors like fibropapillomatosis in sea turtles, systematic cancer studies in wild turtles are almost nonexistent. Following wild turtles across their entire lifespan — which can span more than a human lifetime — is logistically challenging, to say the least.

From Ancient Shells to Modern Medicine

Understanding how turtles keep their cells healthy for so long could eventually help us develop new ways to fight cancer or slow down aging in people. Instead of only studying what goes wrong in cancer, scientists hope to learn what goes right in animals like turtles that stay remarkably healthy for decades or even centuries.

As turtles continue their slow, steady march through evolutionary time, it seems as if they carry secrets in their ancient cells that could help humans (at least one day) do the same.

Disclaimer: This article summarizes the findings of the peer-reviewed paper “Do turtles get cancer?” published in BioScience. It includes carefully framed speculation about how turtle cancer resistance mechanisms might inform future human cancer and aging research. These ideas are early-stage and should not be interpreted as medical facts or direct recommendations for disease prevention or treatment in people. Always consult licensed medical professionals for guidance about cancer screening, diagnosis, or care.

---