Page 111 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

90 PART I The Biology and Pathogenesis of Cancer

TABLE 4.5 Selected Observational Studies of Canine and Feline Cancers by Type of Exposure—cont’d
Exposure Main Findings Strengths/Limitations
VetBooks.ir Zink, 2014 80 Neutering increased risk of developing mast cell tumors, Strengths: Large study size, multivariable analyses were
hemangiosarcoma, lymphoma, and all other cancers in Vizslas
performed.
compared with intact dogs. Neutering at <6 months of age was Limitations: Cases were not histologically confirmed, only
not associated with increased risk of developing cancer compared one breed of dog included.
with neutering at older ages.
Hart, 2014 81 Neutering male golden retrievers and male and female Labrador Strengths: Large study size, Cox proportional hazard
retrievers or at any age had no significant effect on cancer models were used.
occurrence compared with intact dogs; Neutering female golden Limitations: Population limited to dogs visiting a single
retrievers at any point beyond 6 months of age was associated Veterinary Teaching Hospital, only two breeds of dogs
with increased risk of developing any cancer with the exception of included, age categories at time of neutering were not
lymphoma which was associated with an increased risk if consistent among analyses.
neutering occurred before 6 months of age.
Hart, 2016 117 Cancer occurrences in this population of German shepherd dogs were Strengths: Large study size, Cox proportional hazard
rare and there were no associations reported between neutering models were used.
at any age and cancer outcomes. Limitations: Population limited to dogs visiting a single
veterinary teaching hospital, only one breed of dog
included, potential data quality issues.
Diet
Perez Alenza, Higher intake of red meat (as percentage of total calories) was Strength: Used biomarkers of exposure; multivariable
1998 118 positively associated with canine mammary carcinoma risk. analyses included covariates for body conformation.
No differences were observed for intake of fruits and vegetables, Limitations: Use of a retrospective study design is not
or biomarker levels of selenium, retinol, or individual fatty acids. recommended for evaluating biomarkers of exposure
and cancer risk because of possible disease and/or
treatment effects on the biomarker measurement.
Sonnenschein, Higher intake of fat and table food (as percentage of total calories) Strengths: Cases and controls were matched by age, spay
1991 75 was inversely associated with canine mammary carcinoma. No status, and breed size, thus reducing the opportunity for
associations were observed with protein or carbohydrates intake. confounding by these factors; the dietary assessment
tool was validated using a 7-day food record,
Limitations: Study size was too small to evaluate diet-
cancer associations in subgroups.
Raghavan, Vegetable intake (≥3 versus 0 times/week) was inversely associated Strengths: Histopathology and/or cytology confirmation; use
2005 119 with TCC of the urinary bladder in Scottish terriers. A trend was of a comprehensive dietary questionnaire; multivariable
observed with greater servings of vegetables per week and analyses.
decreased risk of TCC. No association was observed for weekly Limitations: Used a volunteer population; 61% of the cases
vitamin supplement intake, compared with no intake. were deceased at the start of the study; 24% of control
dogs had neoplastic diseases.
Body Size
Perez Alenza, Obese body condition at 1 year of age and at 1 year before diagnosis Strengths: Objective measurements of weight and height
1998 118 was positively associated with canine mammary cancer, compared were collected at presentation; body conformation was
with normal or underweight body condition at the same time determined by a clinician at presentation.
points. Limitations: Height, weight, and body conformation at 1
year of age and 1 year before diagnosis were based on
owners’ reports.
Sonnenschein, Spayed dogs that were thin at 9–12 months of age had a lower Strengths: Cases were limited to mammary carcinoma or
1991 75 risk of mammary cancer. Intact dogs that were not overweight adenocarcinoma; designed to assess a timely hypothesis
in adulthood had a lower risk of mammary cancer. that early life factors are related to mammary cancer risk.
Limitations: Controls may not be representative of the
base population; subgroup analyses did not have ample
statistical power to calculate precise measures.
Weeth, 2007 45 BCSs ≥6 were inversely associated with canine cancer risk (all Strengths: Very large study size; 9-point BCS determined
cancers, sarcomas, and carcinomas), compared with BCSs of by physical examination; analyses were conducted by
4–6. BCSs <3 were inversely associated with canine sarcoma risk, cancer type (sarcoma, carcinoma, round cell tumors)
compared with scores of 4–6. Limitations: Selection of cases and controls depended
on availability of BCS in medical records; the inverse
associations with higher BCS may be a result of reverse
causation.