Cancer is a disease characterized by the uncontrolled growth and spread of abnormal cells. Cancer disrupts normal cell growth and division, leading to the formation of tumors or abnormal blood cells. These abnormal cells can invade nearby tissues and, in some cases, spread to distant parts of the body through metastasis. The question of whether all animals can develop cancer highlights a biological vulnerability across diverse life forms.
Cancer Across the Animal Kingdom
Cancer is observed across the animal kingdom, affecting a vast range of species from invertebrates to mammals. Every multicellular organism shares this susceptibility to uncontrolled cell growth. This indicates cancer is inherent to multicellularity, arising from complex processes of cell division and cooperation.
Cancer prevalence and types can vary significantly between species. Domestic animals like dogs and cats are frequently diagnosed with various cancers, many similar to human cancers. Cancer has been documented in fish, birds, some reptiles, and even clams, which can develop a form of leukemia. Studies show that while cancer rates generally increase with body size, this rise is slight, suggesting larger animals have evolved mechanisms to suppress cancer. No animal is entirely immune; even species with low observed cancer rates still exhibit some incidence.
Nature’s Cancer Fighters
Some animals possess resistance to cancer, offering insights into potential defense mechanisms. The naked mole-rat, a subterranean rodent, exhibits longevity and resistance to cancer, with very few instances observed in large colonies. This resistance is attributed to their fibroblasts secreting extremely high molecular weight hyaluronan (HA), a viscous substance over five times larger than in humans or mice. This high molecular weight HA accumulates due to decreased activity of HA-degrading enzymes and a unique hyaluronan synthase 2 (HAS2) sequence, creating an environment that inhibits tumor growth.
Elephants demonstrate a low cancer rate despite their large size and long lifespan, a phenomenon known as Peto’s Paradox. This resistance is linked to their genetic makeup, having multiple copies of the TP53 gene. Humans typically have two copies of TP53, a tumor suppressor gene, but elephants possess at least 20 copies from each parent. These extra copies enhance their cells’ response to DNA damage, triggering cell death in potentially cancerous cells before tumors develop. While sharks are rumored to be immune to cancer, evidence does not support this claim; they can develop tumors, though their unique biology may offer some protective factors.
Influences on Animal Cancer Development
Various factors contribute to cancer in animals, including environmental exposures, genetic predispositions, age, and infectious agents. Animals sharing environments with humans, such as pets, are exposed to similar environmental contaminants. Pollutants like cigarette smoke, industrial emissions, and pesticides can introduce carcinogens and damage DNA. UV radiation from sunlight is another environmental factor linked to skin cancers in animals.
Genetic factors play a role, with certain breeds showing predispositions to specific cancers. For instance, large breeds like Great Danes and Saint Bernards are more prone to bone cancer, while Boxers are susceptible to mast cell tumors and brain tumors. These breed-specific risks stem from inherited genetic mutations or limited genetic diversity within a population. Age is a factor, as cancer risk generally increases with an animal’s age due to the cumulative effects of DNA damage and cell replication errors over time.
Infectious agents, certain viruses, can also induce cancer in animals. For example, feline leukemia virus (FeLV) is a known cause of cancer in cats, with many infected cats developing the disease. Similarly, some papillomaviruses can lead to tumor formation in animals like horses and dogs. Transmissible cancers, such as Devil Facial Tumor Disease (DFTD) in Tasmanian devils, are rare but notable examples where cancer cells are transferred between individuals through biting.
Lessons from Animal Cancer Research
Studying cancer in animals, a field known as comparative oncology, offers insights into cancer biology and its evolution. Researchers can examine naturally occurring cancers in companion animals like dogs, which often develop similar cancer types to humans and share comparable environments. This allows for assessing novel therapies and diagnostic techniques, bridging the gap between laboratory models and human clinical trials.
Animal cancer research contributes to understanding the shared biological pathways involved in tumor development across species. For example, investigating the unique cancer resistance mechanisms in species like naked mole-rats and elephants can reveal new strategies for preventing or treating cancer in humans. This comparative approach accelerates drug development by identifying promising treatments and biomarkers that could be translated to human medicine. Advancements in understanding animal cancers improve veterinary care and provide a foundation for breakthroughs in human cancer prevention and treatment, benefiting both animal and human health.