Page 110 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 4 Epidemiology and the Evidence-Based Medicine Approach 89

TABLE 4.5 Selected Observational Studies of Canine and Feline Cancers by Type of Exposure—cont’d
Exposure Main Findings Strengths/Limitations
VetBooks.ir Endogenous/Exogenous Sex Hormones

Sonnenschein,
adenocarcinoma.
1991 75 Earlier age at spaying was inversely associated with canine mammary Strengths: Cases were limited to mammary carcinoma or
cancer. Trend of decreasing risk was observed for younger age at
spaying. Limitations: Controls may not be representative of the base
population.
Ru, 1998 76 Neutered dogs, regardless of gender, had a greater risk of Strengths: Histologic or radiologic confirmation; large study
osteosarcoma, compared with intact dogs. size; collected information on potential confounders.
Limitations: Medical conditions of the controls were not
clearly described.
Glickman, Neutered status versus intact was a risk factor for TCC of the urinary Strengths: Cases were histologically confirmed.
2004 44 bladder among Scottish terriers. Limitations: Small study size did not permit for analyses by
age at neutering.
Dias Pereira, No overall association was observed for COMT genotype and canine mam- Strengths: Strong biologic rationale for research hypothesis;
2008 114 mary cancer risk. Older age at mammary cancer diagnosis cases were histologically confirmed.
was observed by COMT genotype. Limitations: Very small numbers in subgroup analyses;
selection methods were not provided; information was
not collected on potential confounders (e.g., hormone-
related exposures).
Cooley, 2002 72 Neutering before 1 year of age increased risk of canine osteosarcoma Strengths: Radiographic or histologic confirmation of cases;
among Rottweilers, regardless of gender. Incidence rates decreased retrospective cohort study design.
with later age at neutering. Reproductive factors (number of litters, Limitations: Low participation rate.
number of live births, age at first pregnancy) were not associated
with osteosarcoma among female dogs.
Stovring, MPA use was positively associated with canine mammary cancer. Strengths: Population-based study design; histologic
1997 42 confirmation of cases.
Limitations: Information was not collected on details of MPA
use (e.g., frequency, dose, age at first use).
Teske, 2002 77 Castration was positively associated with canine prostate cancer Strengths: Strong biologic plausibility.
risk, compared with intact status. Limitations: Only cytology was used to make cancer
diagnosis.
Bryan, 2007 78 Neutered versus intact status was a risk factor for the following Strengths: Histopathologic confirmation of cases; included
canine cancers: TCC of the urinary bladder, prostate carcinoma, analyses by histologic subtype.
prostate adenocarcinoma, and TCC of the prostate. Limitations: Statistically nonsignificant measures were not
presented.
Misdorp, Ovariectomy was inversely associated with feline mammary cancer Strengths: Histologic confirmation of cases; collection of
1991 115 risk. Regular administration of progestogens increased risk. detailed exogenous progestogens (frequency, brand,
No association was observed for irregular progestogen type); large study size.
administration or for parity. Limitations: Cases and controls were selected over different
time periods.
Overley, Intact versus neutered status was a risk factor for feline mammary Strengths: Histologic confirmation of cases; large study
2005 116 cancer. Cats spayed before 1 year of age were at lower risk of size.
mammary cancer than those spayed after 6 months of age. Limitations: Univariate analyses were performed, although
There was no risk benefit in cats spayed after 2 years of age. detailed information was collected on exogenous hor-
mone use, parity, and number of litters; large amount of
missing data because of veterinarian nonresponse.
Torres de la Male golden retrievers were more likely to develop lymphoma Strengths: Large study size.
Riva, 2013 79 when neutered <1 year of age compared with intact dogs; Limitations: Cases were not histologically confirmed, only
Female golden retrievers were more likely to develop one breed of dog included.
hemangiosarcoma when neutered at >1 year of age
Continued