Can we learn more about human cancer from dogs?
The study of cancer through comparative oncology (the study of cancers in both humans and animals), in recent times, has provided invaluable insights on how the pet-dog is not only man’s companion but also plays an integral role in improving human health and well-being. More importantly, reiterating the added value of One Health (which is a collaborative and multidisciplinary approach to solving societal challenges) by acting or having the potential to act as sentinels (early warning systems) and models for studying, early diagnosis and treatment of human cancer.
Cancer is a devastating diagnosis and may have touched us at some point in our lives, either directly as a patient, or as a relative, friend, workmate or owner to a pet (Figure-1) that develops cancer. Worldwide, it continues to torment man and dog alike, with the global burden increasing in both species.
Figure 1: Lung cancer in a dog
In Kenya, cancer ranks as the number three cause of mortality in humans, after infectious diseases and cardiovascular diseases, with the number of cancer cases projected to nearly double by 2030. This has and will continue to escalate the ‘double burden’ of disease, with an accompanying dual effect of not only straining existing health-care systems but also causing loss of income to already poor families and posing cumulative economic losses. The challenge of addressing cancer in Kenya has been attributed to several technical, economic, infrastructural and social factors.
The dog is of special interest compared to other laboratory and domestic animals in studying human cancer, because: it naturally and increasingly develops spontaneous cancer similar to humans, which could be as a result of the increasing ‘human-dog bond’ which increases their exposure to similar risk factors and environmental carcinogens (things that cause/initiate cancer). Moreover, the dog is phylogenetically closely related to man this is supported by the fact that, approximately all the 19000 genes identified in the dog match to a similar gene in the human genome. Astonishingly the clinical signs of cancer in dogs also have a close resemblance to those of humans (see Figure-2).
Figure 2: Clinical signs of cancer
Several studies have documented that pet-dogs respond to a number of environmental carcinogens, similar to the way humans do. For instance, the association between industrial activity and consequent bladder cancer has been established, with the dog having a shorter latent period of bladder cancer (10 years), as compared to
Published work in Nairobi (http://dx.doi.org/10.14202/IJOH.2016.42-57) shows that the common cancers in both male humans and dogs are those of the Prostate, the Respiratory tract, Lymphoma and Liver, while in females they are those of the Breast, Mouth, Liver and Lymphoma (see Figure-3 elaborating on lymphosarcoma). With the breeds commonly affected with cancer being those of the German Shepherd, cross breeds and Rottweilers, this could also be attributed to the high population ownership of those breeds as well.
Figure 3: Brief description of lymphosarcoma
The high cases of prostate cancer in both male humans and dogs could probably be related to testosterone levels, with a lower occurrence in male dogs compared to humans probably due to dog castration/neutering. The high cases of mammary gland cancers in both dogs and
Clinically most cancers would appear as masses (see figure 4) and clinicians are inclined to surgically remove the mass and this is why the surgical method of treatment is a common therapeutic intervention in both humans and dogs to control or eliminate local cancer in an attempt to improve the quality of the patient’s life; while the medical approach is mainly used on palliative basis. Chemotherapy is also used in some cases (or in combination with surgery) mainly to ease pain and provide the highest quality of life in both humans and pet dogs.
Figure 4: Tumour of the mouth in
The co-sharing of some of the cancers by both humans and dogs fortifies that it may be possible to use dogs as models and sentinels in studying human cancers. This, therefore, reiterates the fact that developing joint animal-human cancer registries and integrated cancer surveillance systems may possibly lead to accelerated detection of the risks of cancer, especially in developing countries where cancer incidences have recently been shown to be spiking. This calls for more comparative research in this area in order to empower with information for giving collaborative policy guidelines in cancer prevention and control in both humans as well as animals. Since cancer prevention is one of the primary objectives in the government of Kenya, we (physicians and veterinarians-and their sub-groupings) have a responsibility to advise people and pet owners on the benefit of simple lifestyle changes as a means of reducing the risk of cancer in Kenya and other developing countries as well.
If you work in Veterinary Cancer Registry field, join the Global Initiative for Veterinary Cancer Surveillance https://www.givcs.org/
