Most pet owners know that it is not a good idea to smoke close to your pet since cats and dogs are as susceptible to lung cancer as humans are. But what about those kinds of animals that never come close to any human-made toxic substance?
Do wild animals get cancer? Yes, they do. Whether or not an organism can get cancer depends on whether or not it is composed of more than one cell, or, in one word: multicellular. Cancer is, in short, abnormal cell growth, and therefore having the ability to grow more cells is all an organism needs to be susceptible to cancerous growths, too. While plants can develop tumors, they do not metastasize – spread by moving around – though, since they are held in place by cell walls.
Unicellular organisms – those that consist of only one cell – are typically bacteria, microbes, or plankton. Those are usually so small that you cannot see them under a microscope, so you can consider it as a rule of thumb that everything that is big enough so you can see it can theoretically get cancer.
Cancer develops when old cells do not die any more and instead start growing out of control, forming new, abnormal cells. When these new cells form a mass, it is called a tumor.
Cancer has been around long before humans were. In 2003 researchers screened dinosaur vertebrae for signs of cancer and found signs of several kinds of tumor. Of course, it is close to impossible to find out how these extinct animals developed cancer, but they suspect either a genetic factor or an environmental factor like traces of resin on leaves they consumed.
Since cancer has to do with abnormal cell growth, some people assume that the bigger an animal is and thus the more cells it has, the more it is at risk of developing cancer.
While this sounds logical, it has been disproven. It is such a popular assumption, though, that the fact that big animals do not have a higher propensity for cancer than small animals has got its own term: Peto’s Paradox describes the lack of correlation between animal size and risk of cancer. In fact, some extraordinarily big animals like bowhead whales and elephants only very rarely develop cancer, whereas very small animals like mice are very cancer-prone.
Even animals as tiny as insects can develop cancer, but their naturally very short lifespan usually makes sure that they do not die from it.
Are There Animals That Are Immune to Cancer?
Sadly, no. It has long been assumed that the naked mole-rat was immune to cancer, but this is not true – it just is at very, very low risk of developing cancer. The reason why they are so well protected against the growth of cancerous cells is that naked mole rats produce a lot of high-molecular-mass hyaluronan. Elephants and bowhead whales both have elements in their DNA that protect them from cancer.
Studying these animals’ ways of suppressing and preventing cancer continues to be very useful for medical research.
What Causes Cancer in Animals?
There are genetic factors that lead to some species being more or less susceptible to cancer in the first place, but also environmental factors. Some animals are more sensitive than others when it comes to long exposure to the ultraviolet radiation of the sun, for example, whereas others bask in the sun all day and stay happy and healthy. In humans, as well as in dogs, and horses, skin cancer will lead to the same genetic changes.
In areas close to human habitation, smog, as well as carcinogens in soil and water, like nickel, asbestos, and vinyl chloride are always a risk factor, as are insecticides, pesticides, and herbicides.
In some animals – as well as in humans – the risk of developing cancer gets higher with age, but this cannot be generalized. The elephants and whales mentioned above live a lot older than humans and most other animals – bowhead whales can get about 200 years old! – but still, they are close to immune to cancer.
There are also some viruses that can cause cancer in animals, like feline leukemia, which leads to 30% of all infected cats developing cancer.