Complications of cancer and chemotherapy are often the most difficult for owners. When treating the veterinary cancer patient, the clinician needs to clearly communicate treatment goals with owners. If animals are apparently made worse by the treatment, owners may be reluctant to continue. Because anorexia, nausea, vomiting and diarrhea are obvious outward signs they may be more disturbing than neutropenia, hypercalcemia, lymphadenopathy or other complications. These signs may also be due to the tumor itself and distinguishing what is caused by the treatment and what the disease causes may be difficult. Supportive care should be timely and aggressive.

Long-term complications are described as chronic or lingering problems after the cessation of therapy, while late effects are delayed problems occurring months to years after treatment. Long-term follow-up will not necessarily eliminate chronic or delayed effects of therapy, but it will enable pet owners to make more informed decisions about issues affecting the quality of their pet’s lives. Awareness of risk can encourage changes in behavior that promote health (e.g., proper diet) and early detection of tumor recurrence (e.g., regular veterinary examinations), thus optimizing the chances for long-term survival.

System-specific and/or organ damage, failure, or premature aging due to chemotherapy, radiation therapy, biologic modifiers, surgery, or any combination of the above have been described. Some examples include: 1) cardiomyopathy, renal insufficiency, bladder damage, cataracts, muscle atrophy; 2) compromised immune systems causing increased risk of infection (viral, bacterial or fungal) and possible increased risk of malignancy, 3) damaged endocrine systems leading to thyroid dysfunction, hypothalamic-pituitary dysfunction, or reproductive problems, 4) recurrence and second malignant neoplasms, 5) increased risk associated with certain therapies (e.g., bladder cancer as a result of cyclophosphamide therapy)

Cancer patients have a variety of factors that may predispose them to malnutrition during treatment. Maintenance of optimal weight and preventing nutritional deficiencies (and excesses) can improve the patient's outcome. In addition, nutritional modulation may be beneficial in the treatment of the disease. Therefore, nutrition should be an integral part of the management for every cancer patient.

Researchers have shown that a number of metabolic alterations occur in dogs with cancer. Carbohydrate, protein, and lipid metabolism is altered in dogs with a variety of tumors, although the clinical implications and the affect of diet on these alterations are still being investigated. Whether similar metabolic alterations occur in cats with cancer still needs to be determined. Weight loss or cancer cachexia is a very common problem in people with cancer. Unlike simple starvation in which primarily fat is lost, cancer cachexia involves a loss of both protein and fat. In people, this weight loss is associated with shortened survival and poor quality of life. Two veterinary studies have now shown that weight loss is uncommon in oncology patients. However, some individuals or even certain patient populations may be more susceptible to weight loss. This might include animals undergoing radiation therapy since they often undergo prolonged hospitalization and daily sedation as part of the therapy. A recent study of dogs and cats undergoing radiation therapy showed a median weight loss of 9.4% in dogs and 10.5% in cats. This suggests that preemptive nutrition support may be indicated. When weight loss does occur in the cancer patient, it is important to address this problem. While cancer cachexia is not a common issue in pets, obesity can often be a problem in dogs undergoing chemotherapy. This may be the result of prednisone use as part of the chemotherapy protocol or from owners who indulge their sick pet. In some of these patients, obesity can be severe enough that it interferes with the patient's quality of life (e.g., reduced mobility, musculoskeletal disorders). Early discussion of the problems of obesity with owners is recommended when weight gain is first noted, not after it is too late. It is extremely difficult to convince an owner of a cancer patient to put their pet on a strict reduction diet.

A careful diet history can help to identify the presence and significance of the following factors that put patients at risk of malnutrition (e.g., weight loss, changes in appetite) or overnutrition (e.g., obesity, vitamin or mineral excesses from supplementation). Sometimes a careful diet history will reveal an inappropriate diet, excessive supplementation, or other nutritional problems. Monitoring body weight and body condition throughout therapy for cancer patients is critical. Trends in body weight can identify weight gain or weight loss before it becomes a problem. Body condition scoring provides additional information on whether the body weight is appropriate for that animal (e.g., a 1-9 scale with 5=optimal body condition). Other physical examination findings may indicate the presence of malnutrition (e.g., muscle loss, poor hair coat, poor wound healing) although these signs are not usually seen until a relatively advanced stage of malnutrition. It is much better to identify an animal at risk for malnutrition (e.g., frequent anesthesia, reduced appetite) and prevent malnutrition from occurring that to try to correct it. It is important to ask owners specifically about nutritional supplement use in dogs and cats with cancer. A large percentage of owners whose pets have cancer are administering nutritional or herbal supplements, and they do not always voluntarily provide this information unless specifically asked. One should ask both the types of supplements and the doses being given. This information can help to determine whether the supplement use and the dose are appropriate, and whether any drug-nutrient interactions might occur with other forms of therapy being used.

Many patients undergoing chemotherapy or radiation therapy develop anorexia at some time during the course of the treatment. Anorexia can have direct detrimental effects because it can lead to weight loss. In addition, anorexia is a common contributing factor to an owner’s decision for euthanasia. Appetite stimulation with cyproheptadine or benzodiazepine derivatives is not usually very effective but sometimes may help to get an animal "jump-started" back into eating. Dietary changes can sometimes be helpful for anorectic animals. Switching to a more palatable food may enhance food intake (changing from dry to canned, from canned to dry, or to a different brand of food). Palatability enhancers also can improve appetite (e.g., low salt tomato sauce, honey, yogurt for dogs; tuna juice, cooked meat for cats). Fish oil supplementation, which is high in n-3 fatty acids, also may reduce anorexia in some animals. The method of feeding may also influence eating behavior. A recent study showed that food intake of hospitalized animals improved significantly when they were hand-fed compared to voluntary eating. If the pet will not eat enough per os, however, nutrition support is indicated.

When animals will not eat sufficient food voluntarily, nutrition support techniques are necessary to ensure adequate nutrient intake. Enteral nutrition is the preferred method for nutrition support. Enteral nutrition is safer, more physiologic, and less expensive than parenteral nutrition, and also helps to maintain gastrointestinal structure and function. Enteral nutrition should be used in any patient that will not or cannot voluntarily eat adequate calories orally. Contraindications include vomiting, severe malabsorption, and an inability to guard the airway. A nasoesophageal tube can be used for short-term nutrition support (3-4 days), while esophagostomy or gastrostomy tubes are indicated for long-term management. An esophagostomy or gastrostomy tube can often be coordinated with sedation for other procedures (e.g., diagnostic procedures, surgery, or, anesthesia for radiation). Diets for tubes depend upon the patient and the type of tube being used. Nasoesophageal tubes require a liquid diet, while esophagostomy and gastrostomy tubes are large enough to use either a blenderized pet food or a "critical care" diet (e.g., Hill’s a/d, Topeka, KS; Eukanuba Maximum Calorie, Dayton, OH). Human enteral diets are used by some practices but these are unbalanced for dogs and cats without supplementation. In cases where human enteral diets are preferred, supplementation with protein and B vitamins (for dogs and cats), plus taurine and arginine for cats is required to avoid deficiencies. Although other nutrients in these formulas also do not meet canine and feline requirements, they usually do not cause a problem with short-term use. Other nutrients, such as glutamine, arginine, n-3 polyunsaturated fatty acids, and micronutrients may have pharmacological benefits above and beyond their nutritional requirements, especially in the cancer patient.

If the entire GI tract is non-functional or conditions prohibit the use of enteral nutrition, the other option is to feed parenterally. Parenteral nutrition can be delivered by a central vein (total parenteral nutrition or TPN) or a peripheral vein (peripheral or partial parenteral nutrition or PPN). Although PPN is not a replacement for TPN, it can be useful for short-term nutritional support (< 5 days) in a non-debilitated animal to help prevent malnutrition. It also can be used to supplement tube feeding in some cases. Since PPN can only be formulated to meet 50-75% of a patient’s energy requirements, it should not be used in debilitated patient. Another temporary option for PPN is commercial mixes containing a protein and carbohydrate source (e.g., Procalamine, McGaw, Irvine, CA and Quick Mix, Clintec, Deerfield, IL). Although these solutions only provide approximately 25% of energy requirements when administered at maintenance fluid rates, they can be useful as an interim or short-term source for parenteral nutrition. Like TPN, PPN has potential complications, including metabolic disorders, mechanical complications, and sepsis so careful handling of catheters, lines, and solutions is required. Monitoring for metabolic abnormalities is also necessary to prevent complications from all forms of parenteral nutrition.

The veterinary community is beginning to appreciate the relationship between enteral nutritional support and proper medical and surgical management of companion animals. The optimal route for meeting the nutritional requirements of companion animals is the gastrointestinal tract. Enteral nutritional support uses some part of the gastrointestinal tract to feed the patient that cannot or will not eat but can digest and absorb nutrients. Enteral feeding is the simplest, fastest, safest, and least expensive method of feeding companion animals that require nutritional support. Assessment of the patient requiring enteral nutritional support should include an assessment of the animal, the current diet, and feeding management. The combined subjective and objective data collected can be used to formulate an appropriate enteral feeding plan and define the specific nutritional goals to manage the patient. The feeding plan then must be implemented and monitored and if the animal goes home with an enteral tube the client must be educated. Frequently the veterinarian must rely on clinical judgment, rather than on objective data, to decide to institute enteral nutritional support. However, simple tools such as thorough clinical assessment are surprisingly sensitive. The primary goal of nutritional assessment is to predict the animal that can benefit from nutritional support. In the future, other techniques may be available clinically to provide a more objective and quantitative assessment of nutritional status. Anorexia and malnutrition, particularly protein calorie deficiency, is common in companion animals requiring nutritional support. Malnutrition reduces synthesis of plasma proteins, impairs wound healing, and decreases immune response. It is essential for the veterinarian to assess the nutritional status of the patient on initial presentation and to reassess the animal at appropriate intervals after nutritional intervention to determine whether a change in nutritional status has occurred.

Nutritional assessment of the companion animal is a structured process that includes review of the signalment, history and medical record; physical examination; laboratory evaluation; and, estimation of nutritional requirements based on physiological state. Review of the signalment, history and medical record should include questions related to changes in body weight, food intake, and drugs and other therapies that may affect appetite and/or nutrient metabolism. The medical record may provide important objective information that may provide clues to the animal's nutritional status. There are several drug/nutrient interactions that may influence dietary intake or nutritional requirements. For example, animals receiving diuretics may have increased needs for potassium, magnesium, and calcium. The patient's physiological state should be defined by collecting information related to body weight, body condition scoring, growth rate, reproductive status, species, and the nature and duration of the presenting illness. These parameters affect the nutrient requirements of the animal for a given nutrient. Furthermore, the client should be questioned about environmental factors, such as activity and housing, which could also alter nutrient requirements. The client should also be questioned about the animal's dietary history including the current diet, eating habits, and feeding management. The dietary history should strive to identify all items of food being consumed by the animal including table scraps, treats, and supplements. The amount of each food offered and consumed should be specified and factors that could affect intake, such as other animals in the household, should be recorded. Companion animals that have been anorectic or had restricted food intake for longer than 3 days may benefit from nutritional intervention.

Physical examination can help to define the nutritional status of companion animals. Body weight and body condition scoring (score of 1 to 5, with 1 being thin and 5 being obese) provides a subjective estimation of the animal’s body composition. Fat cover over the ribs, down the topline, around the tailhead, and ventrally along the abdomen should be evaluated. Body condition scoring can be combined with zoometric measurements such as pelvic circumference to provide a better estimate of body fat. Body weight can be compared to usual or optimum body weight and to breed standards. Nutritional support is indicated if the patient has recently lost more than 10% of usual or optimum body weight. The patient's general appearance should be assessed including the presence or absence of edema, ascites, and nonhealing wounds. Evaluation of hair coat, skin, and nails may provide an indication of malnutrition. Growth retardation, muscle weakness, or atrophy aids in the identification of catabolic, critically ill patients. Organ dysfunction, such as the liver, heart, kidneys, or lungs may serve to explain poor body weight and condition and will help to define the most appropriate nutrient profile for the enteral diet. Laboratory evaluation may serve as objective indicators of nutritional status, however no single laboratory parameter analyzed routinely in veterinary medicine can accurately assess nutritional status. Laboratory tests such as albumin, lymphocyte count, pack cell volume and total protein may provide insight into the patient's nutritional status. For example, hypoalbuminemia may indicate visceral protein depletion due to chronic undernutrition or protein loss. In humans, hypoalbuminemia correlates with increased morbidity and mortality rates and longer hospital stays. In the future, shorter half-life serum proteins such as prealbumin, transferrin, retinol-binding protein, or fibronectin may be available to assess short-term changes in nutritional status. Serum glucose is important to assess in severely stressed, catabolic patients. Furthermore, since malnutrition affects the immune status of the patient perhaps, in the future, an immune profile could be developed to provide a more sensitive assessment of nutritional status. Serum biochemical profile changes associated with major organ dysfunction may provide indications of problems that may be nutrient sensitive and therefore affect the selection of the enteral diet. For example, if the patient requiring enteral nutritional support has associated renal or liver disease, diet selection would dictate a modification in the levels of certain nutrients. Other laboratory tests that may be of value in nutritional assessment include urinalysis and fecal analysis.

The patient's nutrient and water requirements should be calculated and compared with the nutrient and water intake of the animal. Nutrient intake can be estimated from the dietary history or be monitored and evaluated if the animal is hospitalized. In most cases, the animal requiring enteral nutritional support will have an intake that is less than it’s requirements. Calculation of the nutrient requirements of the patient requiring enteral nutritional support depends on the physiologic state of the animal. Many of these animals will be critically ill, at least initially, and may have suffered traumatic injury, sepsis, or major organ disease in combination with food deprivation. There are many conditions commonly diagnosed in veterinary medicine that increases the animal's risk of malnutrition. Disorders that may be associated with increased losses of protein and electrolytes include vomiting, draining wounds, ileus, diarrhea, abscesses, chylothorax, enteropathy/nephropathy, and malassimilation. Conditions that may be associated with increases or decreases in nutrient requirements include blood loss, liver disease, renal disease, trauma, sepsis, pulmonary disease and cancer. Nutritional support may be indicated in animals that are receiving antinutrients or catabolic drugs that result in anorexia or dysphagia. Cats have special nutritional requirements as compared to dogs because they are strict carnivores. These special dietary requirements of the cat should be considered when considering the selection of an enteral product. Cats have several special physiologic and metabolic requirements compared to dogs including a higher protein requirement; and essential need for taurine; a requirement for arachidonic acid in their diet; a higher niacin and pyridoxine requirement; and, and inability to convert B-9carotene to vitamin A. These differences become important when selecting an enteral product to feed a cat. Human liquid diets are not balanced for cats and many of the products do not contain sufficient taurine.

The following steps should be used to calculate the patient's nutrient requirements (both dog and cat) and feeding level for enteral nutritional support:

Resting Energy Requirement (RER) Resting energy requirement is the amount of energy required by the animal in a post-absorptive resting state and accounts for a thermoneutral environment and physiological influences. In human medicine, RER is determined by indirect calorimetry but this technique is not widely used in veterinary medicine. In critically ill companion animals, the goal is to meet resting energy requirement on a daily basis. Critically ill animals will be hospitalized and confined to a cage and will have energy requirements that are below maintenance levels. Many times patients will not have eaten for several days and therefore should be adapted to the enteral diet over several days. Resting energy requirement is the starting point in meeting daily energy requirements. If the animal tolerates this level of feeding, then energy intake can be increased over time. Patients that are sent home and fed long term through feeding tubes will be fed at higher levels, closer to maintenance levels. Again, goals for energy intake will be dictated by physiological state of the animal. Many of the enteral diets that are fed to dogs and cats, the nutrient content are balanced to the caloric content of the diet. Therefore, if you feed to meet the calculated daily energy requirement of the patient all other nutrient requirements will be met. Water should be provided at the rate of 1ml for each kcal of calculated daily energy requirement.

Diet selection for enteral nutritional support depends on tube size and location, product availability and cost, functioning of the gastrointestinal tract, and the experience of the veterinarian. Products available to feed include blended pet foods, veterinary-formulated critical care diets, and human liquid enteral diets. Pet foods are higher in protein and fat than commercially available human liquid diets; have various nutrient profiles; are readily available; and, are the least expensive products to feed for the enteral support of dogs and cats. Both blended pet foods and veterinary-formulated critical care diet s will cause fewer complications, such as diarrhea, and usually require fewer feedings per day than human enteral diets. In most cases, a high energy and protein food should be chosen as the enteral diet. However, if the patient has renal or liver disease a veterinary therapeutic diet can be blended and fed through the tube. Patient's fed veterinary diets through the feeding tube may be fed the food directly when they have regained their appetite, thereby eliminating a diet change. The veterinary-formulated critical care diets will have increased levels of protein and fat as compared to average maintenance foods to aid in sparing lean body mass and maintain host defenses. These diets may have increased levels of branched chain amino acids, n-93 fatty acids, B-9 complex vitamins, antioxidants such as vitamin E, glutamine, arginine and selected minerals (e.g., potassium, magnesium, and zinc). These diets may be formulated to be fed to both dogs and cats. These types of diets would not be indicated in animals with renal or liver disease or for animals with gastrointestinal problems that have resulted in fat intolerance. Human liquid enteral diets may cause diarrhea when fed to companion animals and the diets are usually more expensive. Furthermore, the human liquid enteral diets are not balanced for cats and must be modified with nutrient modules. Human liquid diets are available in polymeric and monomeric formulations. Monomeric or elemental diets contain nutrients in their simplest forms and require minimal digestion by the patient. Polymeric or meal replacement diets contain mixtures of proteins, fats, and carbohydrates from simple ingredients. Polymeric diets require normal digestion. Human liquid enteral diets have the advantage that they can be fed through small feeding tubes and are available in wide variety of nutrient profiles.

Total food dose (mls). Daily energy requirement (kcals). Energy density of the product (kcal/ml).

Initiate feeding by dividing the total daily amount to be fed by the number of feedings per day. Begin by feeding 1/3 of the food per day and gradually increase the amount of the enteral diet per day. Example feeding schedule for the first three days calculated diet + 2/3 water calculated diet + 1/3 water Full calculated diet (no water added)

Frequency of feeding depends on the diet type, route of feeding (tube type), and digestive/absorptive capacity of the patient. For example, an animal fed through an enterostomy tube may require constant infusion of the diet.

Reassess the patient to determine response to the diet and modify the feeding plan if needed.