Characteristics of the Feline Cancer Population

The impact of diet on neoplastic disease is multi-faceted. Both dietary habits and nutritional status have been found to be risk factors for the development of certain types of cancer. Nutrition, including special diets and specific nutrients, has also been investigated for its therapeutic role in cancer patients. In addition, the response to chemotherapy and tolerance of treatment has been found to be associated with nutritional status.

With the current lack of nutritional investigation specific to feline cancer patients, the focus of this chapter will be on what we know about the clinical presentation of this population, the process of assessing nutritional status in cats, the significance of poor nutritional status in cats affected with neoplasia, and what strategies we currently have at our disposal to intervene in cancer patients who are experiencing anorexia, weight loss, and a decline in body condition.

Kathryn E. MICHEL
DVM, Dipl. ACVN
Kathryn Michel graduated from the school of Veterinary Medicine at Tufts University with a doctorate in Veterinary Medicine in 1983. She completed a residency in small animal clinical nutrition and a master’s degree at the University of Pennsylvania, followed by a postdoctoral fellowship with the Nutrition Support Service at the School of Medicine. She is a diplomate of the American College of Veterinary Nutrition and currently an associate professor of nutrition and chief of the Section of Medicine at The University of Pennsylvania. Her research interests include nutritional assessment, nutritional requirements of hospitalized companion animals, and nutrient modulation of gastrointestinal and endocrine diseases.

Karin U. SORENMO
DVM, Dipl. ACVIM, Dipl. ECVIM-CA (Oncology)
Karin Sorenmo graduated from the Norwegian School of Veterinary Science. She completed a residency in oncology at the School of Veterinary Medicine of the University of Pennsylvania where she is currently an associate professor of oncology and serves as the chief of the Oncology Section. Her main research interests include mammary gland tumors in dogs and cats, and cancer immunotherapy.

The interactions of diet and neoplasia have been much more extensively investigated in human patients, and what preliminary studies exist in veterinary medicine almost all focus on canine cancer patients. Cats, however, do make up a substantial portion of the oncological caseload and one might be tempted to apply findings in other species to the feline patient. This, however, should be done with caution given the many unique aspects of feline physiology, metabolism, and disease. For example, one report found that the minority of canine cancer patients (5%) had an underweight body condition (Michel et al., 2004). Conversely, the clinical impression has been that feline cancer patients are often in poor body condition. A recent investigation at the University of Pennsylvania found this to be the case with 44% of patients assessed as having an underweight body condition and > 90% as having evidence of muscle wasting (Baez et al., 2007) (Figure 1).

Figure 1. Over 90% of feline cancer patients examined in an investigation at the University of Pennsylvania were found to have experienced muscle wasting (Baez et al., 2007). (© K.Michel & K. Sorenmo).

1. Characteristics of the Feline Cancer Population

Cats comprise approximately 26% of all cancer patients seen by the oncology service of the University of Pennsylvania and the fraction of cats versus dogs has remained constant over the past decade. Despite the fact that cats represent a significant portion of patients that undergo treatment through the oncology section, there is limited information regarding the feline cancer population on how nutritional factors might influence treatment and outcome. In order to characterize the feline cancer population better in terms of age, breed, sex, body weight, and what types of malignancies they were treated for, information on all cats with malignancies that were seen by all sections of the Veterinary Hospital of the University of Pennsylvania over the past three years was collected. This population may be representative of the feline cancer population in many other larger urban referral centers.

Epidemiologic Data

A total of 712 cats with a diagnosis of various types of cancer were evaluated. Eighty percent were domestic short hair cats, with a slight over-representation of males versus females (52.7 versus 47.3%) of which all but one cat was neutered. The majority of cats were middle-aged to older, with a mean age of 11 years and a mean body weight of 4.58 kg. Sixty percent of the cats had different types of solid tumors and 40% had lymphoma or leukemia. When comparing cats with solid tumors to cats with lymphoma or leukemia, we found that these two groups differed significantly in age and body weight; cats with solid tumors were significantly older and heavier than cats with lymphoma/ leukemia with a mean age of 12.0 years versus 10.5 years (p< 0.0001) and a mean body weight of 4.7 kg versus 4.4 kg (p= 0.049). This difference is not surprising since most cats with lymphoma present with signs of systemic disease and multi-organ involvement at the time of diagnosis.

Feline Lymphoma

Cats with lymphoma represent a significant portion (40%) of the total hospital feline cancer population and an even higher proportion of the oncology section’s cat population, since many of these are treated with systemic chemotherapy. The original World Health Organization Classification system listed the various anatomic forms as generalized, alimentary, thymic, skin, leukemia (true, i.e., only blood and bone marrow involved) and others (Owen, 1980). A more simplified and practical classification system includes only 4 groups and feline lymphoma is typically classified according to anatomic site: the thoracic form, the alimentary form, the multicentric form, and an unclassified form (skin, leukemia, CNS, nasal etc) (Moore et al., 2001).

Alimentary lymphoma is the most common anatomic form of lymphoma currently seen in our hospital. This is probably also representative of the situation in most other oncology practices since most cats with lymphoma that are diagnosed today are FeLV negative with primary alimentary involvement. Cranial mediastinal lymphoma typically found in FeLV positive younger outdoor cats is not as common anymore (Gabor et al., 1998; Vail et al., 1998; Richter, 2003; Louwerens et al., 2005; Milner et al., 2005). The alimentary forms of lymphoma often pose a challenge to the clinician both from a therapeutic and a nutritional point of view.

Unlike many dogs, cats with lymphoma are typically diagnosed when they have clinical signs from their lymphoma. Systemic signs secondary to lymphoma will constitute a sub-stage B category, which according to many studies is associated with a worse prognosis. In fact, sub-stage B is a more consistent negative prognostic factor in the canine lymphoma literature than stage of disease (Valerius et al., 1997; Baskin et al., 2000; Garrett et al., 2002; Simon et al 2006).

The list of which signs qualify as B-signs has not been completely defined, and leave some room for subjectivity, but in general include any signs of systemic disease at diagnosis, regardless whether these signs are directly associated with the lymphoma, are paraneoplastic, or are from other concurrent illness. Many of these B-signs are typical presenting complaints when cats with lymphoma present for initial evaluation and diagnostics. The typical clinical signs associated with alimentary lymphoma include: decreased appetite, anorexia, vomiting, diarrhea, weight loss and fatigue (Richter, 2003). The clinical signs might have lasted for weeks to months, and many of these cats present in poor nutritional condition. Successful management of these patients requires effective treatment of the underlying malignancy, i.e. chemotherapy, while at the same time controlling nausea, vomiting, diarrhea, anorexia and instituting adequate nutritional support.