Obesity is a growing area of concern for humans and companion animals. Each year, the medical community and popular press dedicate increasing amounts of time and resources to the health complications of obesity in humans, which is currently considered one of the fastest-growing epidemics throughout the world.1 Obesity in humans is associated with an increase in risk of fatality for a number of disease states, and obesity-related deaths are expected to outnumber the causes of death for all other preventable conditions in the near future.2 Diseases associated with obesity in humans include degenerative orthopedic disease, respiratory compromise, heart disease, hypertension, diabetes mellitus, and intervertebral disk disease.2,3 Obesity influences the development of certain cancers, such as colorectal carcinoma,4 postmenopausal breast adenocarcinoma,5 esophageal-gastric adenocarcinoma,6,7 and hepatocellular carcinoma,8 but it does not increase the incidence of premenopausal breast cancer,5,9 and its role in the development of prostate cancer is unclear.10,11 The relationship between obesity and specific types of cancer in humans suggests the potential for a similar association in dogs.
A number of mechanisms have been proposed for the role of obesity in carcinogenesis. Chronic increases in insulin concentrations, which are evident in obese humans, suppress the formation of IGF binding proteins.12 Decreased concentrations of IGF binding proteins allow for greater circulating concentrations of free IGF. In turn, free IGF acts as a cell-growth promoter that suppresses apoptosis of normal and aberrant cells, which leads to a proposed increase in survival of tumor cells.12 Leptin, a hormone produced by adipocytes and therefore found in greater quantities in obese patients, is a promoter of human mammary cancer cells in vitro13 and is implicated in the development of certain hepatocellular carcinomas.8 Obese dogs also have increased circulating concentrations of IGF and leptin,14–16 although an association between these hormones and the development of cancer in dogs is not clear.
Another potential mechanism is the relationship between mutations in tumor suppressor genes (such as p53) and obesity. Mutations in p53 are found in approximately half of all cancers in humans17 and are also found in a number of cancers in dogs, including hemangiosarcomas,18 osteosarcomas,19 and mammary gland tumors.20 In p53-knockout transgenic mice, excess caloric intake and subsequent obesity accelerate tumor development and decrease lifespan, relative to results in mice with a restricted caloric intake that remain lean.21–23
The most common measurement of obesity used in veterinary medicine is the BCS. Body condition scoring evaluates adiposity at designated body sites and scores an animal in relation to a lean musculoskeletal system.a There are 2 BCS scales commonly in use. One uses a 9-point scale, with 4/9 to 5/9 considered an ideal BCS. The other uses a 5-point scale, with an ideal BCS of 3/5. Both scales have similar shortcomings, such as potential differences in assignment of BCS values as a result of variation among veterinarians in scoring24 and variations in breed conformation, but both are noninvasive, inexpensive, readily learned, and easy for owners to understand. Additionally, the ability of the 9-point scale to predict fat body mass has been validated25 relative to more expensive laboratory measurements, such as dual-energy x-ray absorptiometry, and when used correctly, each point above 5 on the 9-point scale represents an increase of 10% to 15% over ideal body weight.a Obesity in dogs has been defined as a body weight > 20% over ideal25; therefore, an animal with a BCS ≥ 7/9 would be considered obese.
Excess body fat mass in dogs has a substantial impact on the development of degenerative orthopedic disease26 and resistance to insulin.27 In 1 study,26 investigators reported an increase of 15% in mean life span for restricted-fed dogs (mean ± SEM BCS, 4.6 ± 0.19 [9-point scale]), compared with life span for control dogs (mean BCS, 6.7 ± 0.19 [9-point scale]). In a study28 on the association between obesity and various diseases of dogs, investigators found an increased prevalence of benign and malignant neoplasms among dogs considered obese. The importance of factors such as obesity on the development of histologically and behaviorally malignant cancers remains controversial despite the prevalence of cancer among the general canine population. With approximately 40% to 50% of dogs older than 10 years of age developing 1 or more types of tumors,29 finding a relationship between obesity and cancer in dogs could serve as a provocative impetus for the avoidance of obesity in dogs. Evaluations of this relationship have focused on specific malignant neoplasms (ie, TCC of the bladder and mammary gland carcinoma)30–33 or have included a number of benign or ill-defined types of cancer.28 To the authors' knowledge, there have not been any published reports in which investigators evaluated obesity prevalence in a large population of dogs with various histologically and behaviorally malignant types of cancer. The purpose of the study reported here was to determine the distribution of BCS values for dogs examined at a large veterinary hospital and to evaluate whether the distribution of BCS values for dogs with histologically and behaviorally malignant neoplasms (cancer case dogs) differed significantly from BCS values for dogs without cancer (noncancer control dogs).
Insulin-like growth factor
Body condition score
Transitional cell carcinoma
Veterinary medical teaching hospital
Prevalence odds ratio
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