Nutritional considerations
After diagnosing cancer, veterinarians are frequently asked whether dietary adjustments should be made. This concern among pet owners was reaffirmed by a recent survey-based study, which found that 25% of owners altered their dog’s primary diet within six months of a cancer diagnosis 8. Nutritional intake in pets with cancer is frequently compromised for several reasons, including changes in food preferences and treatment-related side effects. Appetite alterations are a common concern, with studies reporting a wide range of incidences (17-76%) in dogs depending on the chemotherapy drug used. Additionally, it is well known that chemotherapy can induce changes in taste and smell 9. Early pharmacological intervention from the onset of clinical signs is essential, including the use of appetite-stimulating drugs such as maropitant, mirtazapine, metoclopramide, glucocorticoids and cyproheptadine 10. The development of novel drugs and routes of administration such as mirtazapine transdermal ointment shows promise for managing anorexia and weight loss in cats.
A new ghrelin receptor agonist, capromorelin, has received FDA approval in the USA for use in dogs and cats. The solution, dosed at 3 mg/kg orally q24H, has been shown to cause increased food intake and weight gain in both healthy laboratory and inappetent client-owned dogs 11. Similarly, capromorelin at 1-3 mg/kg q24h caused sustained increases in bodyweight and IGF-1 in cats 12.
Additionally, cancer can disrupt various mediators such as inflammatory cytokines, cortisol, catecholamines, insulin, and glucagon, leading to metabolic dysregulation. This may result in the utilization of muscle aminoacids as a primary energy source over fat, potentially leading to cancer cachexia-anorexia syndrome 13,14. Cachexia is defined as loss in lean body mass, and has been shown to correlate with prognosis in several human cancers. Similar associations have been found in pets with cancer; one study noted that although the prevalence of cachexia in dogs with cancer was low (4%), 69% of dogs had experienced some weight loss, and 35% had mild to severe muscle wasting 15. A study in cats reported cachexia in 6% of cases, while muscle loss was seen in 91% of affected cats 16. Additionally, cats with large cell lymphoma that lost ≥ 5% body weight after one month of chemotherapy treatment had significantly shorter survival times than those that gained or had stable weight 17. Another study assessed the effect of obesity on survival time in dogs with lymphoma or osteosarcoma; although no association between body condition score and survival time was found in animals with osteosarcoma, underweight dogs with lymphoma had significantly shorter survival times than those that maintained or gained weight 18.
The clinical impact of cancer anorexia-cachexia syndrome has increased the interest in developing new diets and drugs to enhance energy intake, increase nutrient absorption, and target metabolic pathways to reverse the catabolic effects, increase muscle mass, and enhance protein synthesis 14. Early detection of this syndrome can be challenging, but, when possible, individualized nutritional intervention can help slow progression and maintain a higher quality of life. For this reason, the dietary history should be carefully analyzed at each clinic visit, including any supplements being given, body condition and muscle condition scores. Based on the clinical concerns of the patient, the veterinarian should then ensure that the diet is complete and balanced.
For pets undergoing chemotherapy, additional considerations may need to be taken into account to promote gastrointestinal health and minimize drug side effects (Figure 5). These often include alterations in dietary fiber type and amount, and ensuring the diet offered has high digestibility. Supplementation with fish oil, which is high in omega-3 fatty acids, can also decrease inflammatory cytokine production and improve cachexia and food intake 19.