Page 102 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

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Epidemiology and the Evidence-Based

Medicine Approach

AUDREY RUPLE, BRENDA N. BONNETT, AND RODNEY L. PAGE

Epidemiology is defined as the study of the distribution and deter- and molecular characterization of tumors), therapeutic interven-
minants of disease in populations. Historically epidemiologic tions (e.g., interventional surgery and targeted, small-molecule
methods were used primarily in veterinary populations for the chemotherapy), and the expanding field of genomics in cancer
investigation of outbreaks and/or epidemics of infectious disease, research. This is attributable in part to the presumption that
yet the philosophies, attitudes, methodologies, and application most clients want care for their pets at a level similar to that they
of epidemiology are in fact more broadly applicable to research themselves receive. Therefore many approaches and interventions
and clinical practice, regardless of species, disease, or discipline. In have been adopted from human medicine and applied to animals
fact, epidemiologic principles form the foundation of evidence- despite considerable gaps in evidence as to their efficacy and/or
based medicine (EBM), an approach to the practice of health care effectiveness in the veterinary clinical situation. In addition, even
that is now well accepted in the human and veterinary medicine where a sufficient quantity of studies is present, the quality and
fields. For a clinician, using the EBM approach involves a com- consistency of reporting is frequently inadequate to allow system-
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mitment to base all decisions on the best available evidence and atic review or adequate comparison between studies. This issue is
to be explicit about the level and quality of evidence on which not unique to oncology and has spawned efforts to improve the
decisions are based. An extensive literature is available on EBM reporting of veterinary studies, with a longer term goal of improv-
and evidence-based practice in the human medicine field (e.g., ing the quality of work. 1–7 To approach a level of care in veterinary
The Cochrane Collaboration [http://www.cochrane.org/]) and oncology truly similar to that in humans, there will need to be an
in the veterinary field (e.g., Evidence-Based Veterinary Medicine increased focus on EBM. Further information and articles perti-
Association [https://ebvma.org/]). The EBM approach can and nent to challenges of applying EBM in practice can be found on
should be applied to all interventions, including diagnosis and the website of the Evidence-Based Veterinary Medicine Associa-
prognosis, choice of preventive and clinical therapies applied to tion (https://ebvma.org) and the Centre for Evidence-Based Vet-
individuals, and decisions about health policy or control programs erinary Medicine (http://www.nottingham.ac.uk/cevm/).
for populations. In this chapter, we focus on quantifying the occurrence of
Pathophysiology forms the basis of our understanding of cancer (incidence, prevalence) and risk factors for cancer (causal
health and disease, but this knowledge, even combined with clin- reasoning, associations). An evidence-based approach to diagno-
ical acumen and experience, is not sufficient grounds for decision sis, prognosis, and selection of therapeutic interventions will be
making across the spectrum of activities of health professionals. proposed, although other authors in this text will present specific
To have confidence that our interventions will be beneficial, we details of diagnosis, prognosis, and therapy for specific cancers.
need to understand that personal and expert opinion are only Rather than presenting an exhaustive or systematic review of the
anecdotal evidence, unless they are based on a valid appraisal of literature in this chapter, we will highlight the relevant literature.
available evidence from the literature. In addition to embrac- Our aim is to provide a guide for the application of epidemiologic
ing the philosophy of EBM, all clinicians must develop the principles to oncology, in general and for clinical practice.
knowledge and skills, such as information management, critical
appraisal, and causal reasoning, that are needed to assess evidence Measures of Disease Occurrence
to determine that their chosen interventions are both efficacious
and effective (see glossary of terms in Table 4.1). Unfortunately, Complete and accurate cancer surveillance data are the founda-
especially in veterinary medicine, there are many gaps in our evi- tion needed to make appropriate conclusions about the burden
dence base, in terms of both validity and relevance of published of disease, to make recommendations for cancer prevention and
studies. control, and for the design of analytic studies to identify causal
In veterinary medicine, in general and in certain special- associations between exposures and cancer risk. Here we cover the
ties including oncology, the trend has been toward a heightened measures used to quantify cancer occurrence such as incidence,
sophistication of practice, including the use of advanced technolo- prevalence, and proportional measures and the types of data used
gies in diagnostic testing (e.g., state-of-the-art imaging techniques to calculate them.

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