Page 1293 - Small Animal Internal Medicine, 6th Edition

CHAPTER 75
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Principles of Cancer

Treatment

GENERAL CONSIDERATIONS PATIENT-RELATED FACTORS

Cancer remains the main cause of death in dogs and possibly It is important to remember that the best treatment for a
cats as well. In some dog breeds, including Golden Retriev- particular tumor does not necessarily constitute the best
ers and retired racing Greyhounds, 60% of the deaths are treatment for a particular patient or the best treatment from
due to cancer. For years, a variety of therapeutic modalities the family’s perspective. The most important patient-related
have been used in dogs and cats with cancer (Box 75.1). factor to be considered is the animal’s general health and
However, until 2 or 3 decades ago, surgery remained the activity or performance status (Table 75.1). For example, a
mainstay of cancer treatment for pets. Today, nonresect- cat or dog with markedly diminished activity and severe
able or metastatic malignancies can be treated with varied constitutional signs (i.e., poor performance status) may not
degrees of success, using some of the modalities listed in be a good candidate for aggressive chemotherapy or the
Box 75.1. repeated anesthetic episodes required for external beam
When evaluating a pet with cancer, the clinician should radiotherapy. Age by itself is not a factor that should be
bear in mind that, in most cases, if given the option, owners considered when discussing cancer therapy with the owner;
will elect to treat their pets. Although euthanasia still the author believes that “age is not a disease.” For example,
remains a reasonable choice in some small animals with a 14-year-old dog in excellent health is a better candidate for
cancer, every effort should be made to investigate treatment chemotherapy or radiotherapy than a 9-year-old dog with
options. More than 60% of human cancer patients have a chronic kidney disease or decompensated congestive heart
life expectancy of at least 5 years, and a sizable portion of failure. Patient-related factors should be addressed before
cancer patients, including those with high-grade lymphoma, instituting specific cancer treatment (e.g., correct the azote-
some acute leukemias, and some carcinomas and sarcomas, mia, improve the nutritional status with enteral feeding).
are cured. Although such numbers are not available for
dogs and cats with cancer, in the author’s clinic, the propor-
tion of cancer patients evaluated for 2- to 5-year follow-up FAMILY-RELATED FACTORS
is increasing.
A major philosophical difference when treating cancer in Family-related factors play an important role in determining
humans versus pets is the concept of cure. Although cure is the treatment to be implemented in pets with cancer. Every
a laudable goal in people, the price paid in terms of toxicity clinician is aware of the impact of the owner-pet bond; this
(and the expenses) makes it difficult to justify such an bond is so important that it often dictates the treatment
approach in pets. In the author’s clinic, quality of life (QOL) approach used in a given patient. For example, owners may
drives the treatments of choice (see later). be so apprehensive about having their dog with lymphoma
Depending on the tumor type, biologic behavior, and receive chemotherapy that they refuse such treatment; thus
clinical stage, a clinician may recommend one or more the optimal treatment is denied to this patient.
of the treatments listed in Box 75.1. However, in addition In the author’s experience, pet owners should be made
to tumor-related factors, many other factors influence the a part of the medical team. If they are assigned tasks to
selection of the optimal treatment for a pet with cancer. perform at home such as measuring the tumor to monitor
These include patient-related, family-related, and treatment- the response to treatment, taking their pet’s temperature
related factors. daily, and monitoring their pet’s performance status, they

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