Animal cancer statistics reveal that one of three dogs and one of four cats will be diagnosed with cancer, and this number appears to be on the rise. Despite the fact that cancer is a leading cause of death in dogs and cats, managing the nutritional needs of dogs and cats undergoing cancer treatment can be particularly challenging.
Successful management requires careful selection of treatment strategies and attention to both the medical and nutritional aspects of the patient. The goal of this presentation is to review some of the basic principles underlying optimal treatment for the small animal cancer patient, with a special emphasis on the central role played by nutrition.
1. Collect complete diet information at every visit to determine whether the diet is optimized. A complete diet history includes the main pet food being provided (or the recipe, if not using a commercial food), but also treats, table food, dietary supplements, and foods used for medication administration. There is usually not a single "best" diet for any cat. The authors typically determine several diets that would be appropriate for an individual cat based on the cat's individual clinical situation (e.g., severity of cardiac disease, clinical signs, physical examination findings, laboratory values, and individual preferences of the cat and the owner). These diets are offered as choices for the owner and for the cat. Once they determine which diet the cat prefers, this diet can be used. Be sure to make specific diet recommendations, not just "a low sodium diet" or "a senior diet." Also, even if the cat is discharged with an optimal diet plan, don't assume that the owner is following these recommendations; at subsequent visits, ask exactly what the owner is feeding, each visit.
2. Body condition and muscle condition scores should be determined for every patient with cardiac disease at every visit. Body weight and body condition score, which primarily assesses body fat, are important because they have been associated with overall survival. Although body condition score < 4/9 is relatively uncommon in companion animals with cancer, pre-diagnosis weight loss often occurs. It also is critical to assess muscle condition at every visit, particularly in dogs and cats with cancer, in which muscle loss is common. The muscle condition score is a subjective score which assesses muscle condition in the areas of the epaxial, gluteal, scapula, and temporal areas and graded as normal muscle condition or mild, moderate, or severe muscle loss. Because of increased production of inflammatory cytokines, in congestive heart failure (CHF), muscle is lost preferentially to fat. Therefore, even in overweight animals, significant muscle wasting can be present. This muscle loss has important clinical implications as it negatively impacts strength, immune function, wound healing, and survival. By assessing muscle condition at every visit, muscle loss can be identified at its early stages when intervention is more likely to be successful. Optimizing diet (e.g., ensuring nutritionally balanced diet with adequate calorie and protein intake) and omega-3 fatty acid supplementation can help to reduce muscle loss.
3. Be sure to ask the owner about dietary supplements, since supplement use is very common in dogs and cats with cancer (> 50% in one study). Owners often don't consider supplements a drug or a part of the diet, so they usually do not provide this information unless specifically asked. Therefore, it is important to ask at each visit if the owner is administering dietary supplements. If so, ensure that the supplements are safe, are not interacting with the diet or medications, and are being administered at an appropriate dose. In addition to safety and efficacy issues, there are significant concerns about the quality control of dietary supplements, since they do not require proof of safety, efficacy, or quality control to be marketed. Therefore, careful selection of type, dose, and brand is important to avoid toxicities or complete lack of efficacy.
4. Be proactive with nutritional support. Monitoring body weight, body condition score, and muscle condition score helps to identify if an animal with cancer is eating an appropriate number of calories. In addition, the diet history helps to identify if the calories are optimized. If an animal is not maintaining weight and food intake cannot be easily increased, assisted nutrition is needed. Clinicians should also be proactive in preventing situations in which a patient loses weight. For example, an animal being treated for an oral tumor will likely need a feeding tube to maintain optimal nutrition. Similarly, animals undergoing radiation therapy for a tumor and which require daily anesthesia often lose weight, so careful attention to feeding orders and body weight is needed. Many patients undergoing treatment for cancer develop anorexia (loss of appetite), hyporexia (decreased food intake), or dysrexia (changes in food preferences) at some time during the course of the treatment, and these issues can have direct detrimental effects by contributing to weight loss. In addition, reduced appetite is a common contributing factor to an owner's decision for euthanasia.
Dietary changes or appetite stimulants can sometimes be helpful for animals with appetite issues. Fish oil supplementation, which is high in n-3 fatty acids, also may have modest benefits for appetite in some animals. However, if nausea is being adequately addressed and the animal still will not eat enough voluntarily to maintain weight, assisted nutrition techniques are indicated. Enteral nutrition is preferred because it 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 nasogastric tube can be used for short-term nutrition support (3–4 days), while esophagostomy or gastrostomy tubes are indicated when assisted feeding is needed for longer periods of time. An esophagostomy or gastrostomy tube can often be coordinated with sedation for other procedures (e.g., diagnostic procedures, surgery, or, anesthesia for radiation).
5. Most owners whose pets are diagnosed with cancer consult the Internet for advice on nutrition and other aspects of treatment. Unfortunately, the information on the Internet is virtually unregulated, and its quality ranges from excellent to pure quackery. Sites describing "the best diet for a pet with cancer," "beneficial" dietary supplements, or home-prepared diets that will "help fight cancer" abound. A recent study evaluating diets recommended for animals with cancer found that none were nutritionally balanced! Therefore, deciding which websites are trustworthy can be difficult for owners. Providing owners with good, accurate websites that they can use is important.
It is also important to address common questions, such as low carbohydrate diets, supplement use (especially during treatment), and use of home-prepared diets. Many owners benefit from a consultation (either directly, or through the primary care veterinarian or veterinary oncologist) with a board-certified veterinary nutritionist (www.acvn.org or www.esvcn.eu/college).
6. Encourage adequate food intake by managing nausea.
One critical method of encouraging adequate caloric intake is to anticipate chemotherapy-induced nausea. Nausea and vomiting can result from any chemotherapy drug, but that induced by doxorubicin is quite predictable in the dog. My current protocol for prevention of doxorubicin-induced nausea and vomiting in dogs is to routinely administer injectable maropitant (Cerenia® 1 mg/kg SQ) concurrently with doxorubicin and at home orally (2 mg/kg) for 4 days after doxorubicin administration. If a particular chemotherapy agent typically causes nausea or vomiting in dogs, I follow a similar protocol. In cats, doxorubicin-induced nausea and vomiting are less predictable, and I do not routinely administer maropitant.
For unanticipated chemotherapy-induced nausea and vomiting, I have owners keep medication at home with instructions to administer the medication if vomiting and nausea are severe. For dogs, I prescribe oral maropitant. In my hands, cats are not particularly receptive to oral maropitant. For that reason, I either prescribe injectable maropitant in premeasured syringes or dolasetron (Anzemet® tabs 0.6 mg/kg IV cats q12h. Injectable 0.6–1 mg/kg q12h).
7. Prevent chemotherapy induced diarrhea.
Another gastrointestinal complication of chemotherapy is diarrhea and/or colitis. Any chemotherapy drugs can induce this complication, but doxorubicin, vincristine and toceranib phosphate (Palladia®) commonly cause diarrhea. Coaching pet owners to limit the introduction of new foods to their pet's diet during chemotherapy helps to prevent diarrhea, but when pets refuse to eat, most pet owners have a difficult time not offering a variety of new pet foods and tasty human foods which can cause serious diarrhea. If owners feel they must feed human food, I encourage them to feed bland, easily digestible foods, such as poached white meat chicken and white rice.
Another simple method of limiting diarrhea/colitis from chemotherapy is to feed probiotic agents. Probiotics help maintain "good" gastrointestinal flora despite the damage to the gastrointestinal mucosal by chemotherapy agents. Some owners like to feed yogurt with live cultures; others prefer to feed commercially available products like FortiFlora®, Prostora® or Bene-Bac®. I don't favor one product over another.
I also have the owners keep a seven-day supply of metronidazole (10–15 mg/kg q12h PO) at home to treat a mild episode of chemotherapy induced diarrhea. I encourage pet owners to call me if the diarrhea has not improved after one or two days on metronidazole and to come to the emergency room if the diarrhea is severe or bloody.
8. Keep iron deficiency anemia in mind.
Nonregenerative anemia is common in pets with cancer. Veterinary oncologists see anemia from chronic disease, the effects of chemotherapy and radiation therapy on the bone marrow and blood loss from surgery or tumor induced hemorrhage. While iron deficiency anemia is uncommon, patients with mast cell tumors, gastrointestinal tumors and nasal tumor with ongoing epistaxis may develop iron deficiency anemia. A sensitive and specific test for iron deficiency in dogs and cats is not available, but microcytic, hypochromic anemia is the laboratory hallmark of iron deficiency anemia. In an oncology patient with progressive anemia and a tumor likely to cause blood loss, I will typically administer iron dextran (10 mg/kg IM q30days). If one or two doses of iron dextran does not improve the anemia or result in reticulocytosis, then I discontinue administration.
9. Evaluate patients for B12 (cobalamin) deficiency.
An ill or geriatric patient is at risk for hypocobalaminemia. Hypocobalaminemia occurs as a consequence of gastrointestinal, pancreatic and occasionally thyroid disease and at least in dogs with lymphoma is a negative prognostic indicator. Measurement of B12 levels is a readily available test to determine the need for supplementation. Supplementation recommendations can be found at http://vetmed.tamu.edu/gilab/research/cobalamin-information. Pet owners can easily learn to administer B12 injections at home.
10. Control pain that prevents adequate food intake.
Pain, whether from arthritis, the primary tumor, metastatic lesions or as a result of radiation or surgery, negatively impacts the quality of life. For pet owners, quality of life assessment often involve appetite and play, two behaviors negatively impacted by pain. Each time a cancer patient is seen at the clinic, an assessment of pain should be made, but questioning owners about pain-related behaviors such as limping and licking but also about appetite, activity and sleep, which are often abnormal in painful pets. In dogs, nonsteroidal antiinflammatory drugs are my first line of therapy for pain, and I will add tramadol (4–5 mg/kg PO q6–12h) if NSAIDS do not adequately control pain in dogs. Buprenex (0.1 ml sublingual q6–12h) works well in cats to control pain, and recent reports suggest gabapentin (6.5 mg/kg PO q12h) may also be efficacious.
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8. World Small Animal Veterinary Association Global Nutrition Committee. WSAVA nutrition toolkit. www.wsava.org/nutrition-toolkit (body and muscle condition score charts, feeding guidelines, effective internet use for owners, diet history forms, calorie requirements for dogs and cats, recommendations for selecting a pet food, etc.).