Studying cancer in animals offers new insight into human tumors

The Catalan Institute of Oncology (ICO) and the Bellvitge Biomedical Research Institute (IDIBELL) promote the study of certain cancers in animals. Specifically, tumors caused by infectious agents such as papillomaviruses and the Helicobacter pylori bacteria.

This lets us see if a virus or bacterium behaves differently in different animals, to better understand the pathophysiology and decipher the mechanisms that make some infected individuals eliminate it without problems and in others it causes a tumor.

Cancer in animals

Several studies have shown that wild animals have a much lower cancer rates to domestic or captive animals. Part of this increased prevalence of cancer could be explained because captive animals tend to live longer, which favors the appearance of tumors.

However, it has also been seen that animal populations under environmental stress, either by exposure to toxic, being confined, etc.. also have much higher rates of cancer than wild populations. "In nature, the presence of cancer in animals is very exceptional. Autopsies performed in parks, for example, show that very few wild animals die of cancer or with cancer," says Ignacio González Bravo, from the Infections and Cancer lab. at ICO-IDIBELL.

Moreover, approximately 20% of human cancers are caused by infectious agents. The human papillomavirus is a necessary cause for the development of cervical cancer and is involved in other tumors such as the anus, penis, vagina, vulva and oropharynx. Similarly, Helicobacter pylori promotes the occurrence of gastric cancer, and hepatitis C virus promotes liver tumors.

The ICO-IDIBELL, in collaboration with different institutions worldwide, has analyzed the presence of infectious agents in cancerous tumors horse penis, genital tumors in dolphins, whales, zebras or wild chamois, or in healthy animals without injury like bats or hyenas.

"We do not know what proportion of animal tumors is caused by infectious agents, but in most animals analyzed presented infectious agents that could be carcinogenic" adds Gonzalez Bravo.

Animal study to better understand human tumors

The study of animal tumors allows us to observe if a virus behaves differently in different animals, and better understand its pathophysiology. "We know that, in humans, a variant of the same virus in different cells causes various diseases. If we study what happens in different animals we will understand better how the virus works and how we can fight it."

30% of penile cancer in humans is caused by the same types of human papillomavirus that cause cervical cancer virus. The ICO-IDIBELL research has found that, in horses, for example, the types of papilloma viruses that cause cancer are very different from these. "We are now studying whether part of human penile tumors may be associated with the same variants that cause cancer in horses."

The study in cows has detected a virus that causes gastrointestinal tumors, especially when the cow eats ferns. "The virus and ferns do not cause cancer separately but together they can. Now we have to see if something similar happens in human tumors."

Another point of interest is cancer in large animals such as elephants or whales and what is known as Peto's paradox, which shows that the incidence of cancer is not related to the number of cells having a body. It seems that a large organism with many cells should have more cancer than small animals, with far fewer cells, since the likelihood that a cell becomes cancerous increases each time the cell divides. The reality, however, is that the incidence of cancer is similar. "We must consider whether the large animals have evolved control mechanisms. If we learn how they work, we could develop new tools to fight the disease," concluded Gonzalez Bravo.