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PET DOGS POISED TO ADVANCE CANCER PREVENTION RESEARCH
“Lassie,” “Toto,” and Fellow Pet Dogs: Poised to Lead the
Way for Advances in Cancer Prevention
Deborah W. Knapp, DVM, Deepika Dhawan, PhD, and Elaine Ostrander, PhD
OVERVIEW
Cancer causes substantial morbidity and takes the lives of over 8 million people worldwide each year. Advances in cancer prevention
research are crucial, and animal models are key to this. There are many valuable experimentally induced cancer models, but these do
not fully meet the needs for cancer prevention studies. Pet dogs with risks for naturally occurring cancer can fill important gaps in
cancer prevention research. Using invasive urothelial carcinoma (iUC) as an example, the advantages of utilizing pet dogs include: (1)
close similarities between dogs and humans in carcinogenesis, molecular and cellular features, invasive and metastatic behavior, and
response to treatment, thus providing high relevance for comparative studies, (2) shared environment between dogs and humans to
help identify not-yet-known environmental iUC risks, (3) strong breed-associated risk (5- to 21-fold increased risk compared with mixed
breeds) that facilitates investigation of gene-environment interactions, screening, and early intervention, (4) large size of dogs (versus
rodents) that allows collection of fluids and tissues via cystoscopy, and detailed imaging at multiple time points, and (5) acceptance
for studies in which each participating dog can benefit while enjoying life in their family environment, and in which findings will help
other dogs and humans. An ongoing 3-year study in Scottish Terriers (comparable to a 15- to 20-year study in humans) is aimed at
defining genetic and environmental risk factors for iUC, effective methods for screening/early detection, and a successful secondary
cancer prevention approach with very promising results to date. Pet dogs can indeed propel cancer prevention research.
There is a need for improved cancer prevention research.
More than 580,000 people in the United States and over
8 million people worldwide are expected to die from cancer,
including all cancer types, yearly. 1,2 Although it is accepted
that cancer prevention should offer the most cost-effective
and appealing long-term strategy to control cancer, cancer
prevention research has not kept up with the need, especially
for an aging population. 3 One of the challenges in cancer prevention
research is the identifıcation and use of relevant animal
models in which fındings in the model will actually
translate into improved prevention and treatment strategies
for humans. Unfortunately, many preclinical models fail to
reflect the disease in humans. 4-7 Other published concerns
with experimentally induced models include: (1) the induction
of cancer in animals that are young and otherwise
healthy, whereas humans with cancer are often older with comorbid
conditions, (2) the assessment of response in animals
with homogeneous tumors versus that in humans
with heterogeneous cancer, (3) timing of an intervention
in animals that is unrealistic in humans, and (4) the use of
toxic doses of treatment agents to achieve a desired outcome
in animals when these doses would not be tolerated
by humans. 6
CANCER PREVENTION RESEARCH AND THE VALUE
OF PET DOGS
Strong Potential Value for Pet Dogs in Cancer
Research
There is growing evidence that pet dogs with specifıc forms of
naturally occurring cancer can serve as highly relevant models
for those cancers in humans. 8-12 There are an estimated 83
million pet dogs in the United States, 13 and a quarter of older
pet dogs are expected to die from cancer. 8-12 For specifıc types
of naturally occurring cancer, including, but not limited to,
invasive urinary bladder cancer, 8 osteosarcoma, 14 subsets of
squamous cell carcinoma, 9 and lymphoma, 15,16 considerable
similarities have been noted between the cancer in dogs and
humans in regards to histopathology, molecular features,
and biologic behavior. Importantly, these cancers develop in
the context of an intact immune system, and are characterized
by considerable heterogeneity within and between individuals,
similar to human cancer. 10 Studies to date indicate
that the genes and pathways involved in cancer development
in dogs are similar to those in humans. 17,18 Dogs develop cancer
in an environment shared with their owners, and this has
enabled dogs to serve as sentinels for specifıc carcinogens
such as asbestos exposure and mesothelioma risk. 19 Studies
From the Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN; Purdue University Center for Cancer Research, Purdue University, West Lafayette, IN; National Human
Genome Research Institute, National Institutes of Health, Bethesda, MD.
Disclosures of potential conflicts of interest are found at the end of this article.
Corresponding author: Deborah W. Knapp, DVM, Purdue University, Department of Veterinary Clinical Sciences, 625 Harrison St., West Lafayette, IN 47907-2026; email: knappd@purdue.edu.
© 2015 by American Society of Clinical Oncology.
asco.org/edbook | 2015 ASCO EDUCATIONAL BOOK
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