Cachexia is a significant loss of muscle and adipose tissue. It occurs in patients with advanced cancer, chronic obstructive pulmonary disease, chronic infection including AIDS and tuberculosis, chronic heart failure, and rheumatoid arthritis. Increases in pro-inflammatory factors characterize cachexia. There is a decreased quality of life, decreased tolerance to surgical or medical interventions, and shortened survival.
Cachexia is not simple starvation where fat stores replace glucose as the primary fuel. Cancer causes a change in metabolism as opposed to an energy deficit, so conventional nutritional support is not effective.
Cancer-related cachexia can be broken down into 3 categories:
The causes of cachexia can be related to the disease, treatment, or emotional distress. Nausea, early satiety, and dysgeusia are factors in anorexia.
Mediators of cachexia associated with cancer include tumor necrosis factor-alpha, interleukins (IL) 1 and 6, ciliary neurotrophic factor, and leukemia inhibitory factor, and interferon (INF)-gamma. These produced by tumor cells and host immune cells. These are procachectic factors, as they lead to anorexia, weight loss, protein, and fat breakdown, an acute-phase protein response, falls in insulin level, insulin resistance, rises in levels of cortisol and glucagon, fever, anemia, and elevated energy expenditure.
Host immune cells including macrophages, T-helper-one cells, and myeloid-derived suppressor cells produce procachectic cytokines.
Many tumors cause an elevated adrenergic state that results in an increased rate of energy expenditure. Skeletal muscle is the primary s as part of a persistent inflammatory response. Tumors only produce proteolysis-inducing (PIF) factor. Tumor necrosis factor (TNF)-alpha and PIF induce cachexia by activating nuclear factor kappa B transcription factor found in muscles.ite of lean body mass depletion. This is secondary to increased protein turnover without equivalent protein synthesis.
The JAK/STAT3 pathway is strongly activated by the IL-6 family ligands. STAT3 activation by IL-6 is necessary for muscle wasting. Inhibition STAT3 pharmacologically using STAT3 or JAK inhibitors reduce muscle atrophy. This indicates that STAT3 is a primary mediator of muscle wasting when there is high IL-6 family signaling.
Anorexia and weight loss in cancer patients do not correlate with serum levels of circulating IL-1, IL-6, IFN-gamma, and TNF-alpha. There may be a central mechanism of action producing of cachexia. Cytokines postulated to be involved include TNF-alpha, IFN-alpha, IL-1, IL-6, IL-8, and others.
Serotonin and dysfunction of neuropeptidergic circuits may be involved. Elevated plasma-free tryptophan was observed in patients with cancer and anorexia. This elevates tryptophan levels in the cerebrospinal fluid resulting in increased synthesis of serotonin. Elevated levels of serotonin contribute to cancer anorexia.
Insulin and Ghrelin
Insulin and leptin levels are proportional to body fat content. Central nervous system (CNS) concentrations are proportional to plasma levels. Insulin secretion increases as weight increase. This occurs at the basal state and in response to meals. Leptin is more involved in CNS control of energy homeostasis than insulin. Leptin deficiency causes obesity with hyperphagia. This persists despite high insulin levels.
Ghrelin function is a peptide produced by ghrelin cells in the gastrointestinal (GI) tract and acts in the CNS. Ghrelin is secreted when the stomach is empty. Secretion stops when the stomach is stretched. Ghrelin acts centrally to increase hunger, gastric acid, secretion and gastrointestinal motility. The same brain cells have receptors for ghrelin and leptin, with opposing effects.
Alimentary Tract Dysfunction
Cancer patients often have abnormalities in the taste and smell. Oral intake may be impaired by tumors of the mouth, neck, esophagus, stomach. Obstruction can occur to tumors of the pancreas, liver, and peritoneum. Intestinal obstruction is common. Enzymatic insufficiency secondary to pancreatic insufficiency may contribute to malabsorption. Lymphoma of the intestine or mesentery can result in issues.
Slowing of peristalsis and delayed gastric emptying contributes to early satiety. Chemotherapy commonly causes nausea vomiting, mucositis, and abnormal perception of taste. Stomatitis, alterations in taste and smell, and xerostomia often occur secondary to radiotherapy to the head and neck. Abdominal radiation therapy can cause nausea, vomiting, anorexia, diarrhea, and malabsorption.
Biochemical and Metabolic Derangement
Neoplastic cells have high levels of glucose utilization and production of lactic acid, the Warburg effect.Hexokinase is the first step of the glycolytic pathway and overexpressed in tumor cells contributes to this process. Tumor glycolysis and host gluconeogenesis may be an important cause of cancer cachexia.
Recently, an extensive re-examination of Warburg effects shows that unlike the majority of cells, numerous cancer cell lines obtain a significant portion of their energy from aerobic glycolysis. Many malignant cells secrete hydrogen peroxide, oxygen free radicals drives mitophagy, aerobic glycolysis, and autophagy.
Theorized Causes of Cancer Anorexia
Orexigenic and Anorexigenic Neuropeptides
(Ref: Ohnuma, T. Anorexia, and cachexia. In: R. C. Bast, Jr., C. M. Croce, W. N. Hait, W. K. Hong, D. W. Kufe, R. E. Pollack, R. R. Weichselbaum, J. F. Holland, Eds. Cancer Medicine (9th Edition). John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, 2017, in press)
The cachexia prevalence ranges from 5% to 15% in congestive heart failure (CHF) or chronic obstructive pulmonary disease (COPD) to 60% to 80% in advanced cancer. Mortality rates of patients COPD and cachexia are 10% to 15% per year. In patients with cachexia and CHF or chronic kidney, disease mortality is 20% to 30% per year, and it is 80% in patients in cachectic cancer patients.
The multiple signaling pathways that cause muscle atrophy are interdependent. Inhibition or activation or inhibition of a single pathway often causes a cascade affecting muscle protein balance.
Reactive Oxygen Species and Oxidative Stress
Cancer cachexia results in metabolic reprogramming of muscle and adipose tissues. Fatty acids are catabolized by cancer cells to provide energy for tumor growth. Invasion of adipose tissue by cancer cells induces the release of free fatty acids from adjacent adipocytes. Autophagy and lysosomal degradation result in muscle wasting. HSL and ATGL knockdown studies reveal that they mediate muscle degradation.
There is selective parasitism by the tumor of the host. There is competition for substrates with tumors acting as nitrogen traps independent of protein intake. Given that the total tumor mass in most patients is usually less than 550 g and that patients with very small tumors can have cachexia, it is doubtful that simple competition for nitrogen is responsible for cachexia.
The definition of cancer cachexia includes weight loss of more than 5% over 12 months, BMI of less than 20, or sarcopenia as evidenced by dual-energy x-ray absorptiometry.
Stages of Cancer Cachexia
In pre-cachexia, there is anorexia and metabolic change with a weight loss of 5% or less.
In cachexia, the BMI is less than 20, weight loss is more than 2%, or systemic sarcopenia and weight loss more than 2%.
In refractory cachexia, the cancer is usually unresponsive, performance score is low, and predicted survival is less than three months
(from Ref. Fearon K, Strasser F, Anker SD, et al. Definition and classification of cancer cachexia: an international consensus. Lancet Oncol 2011;12:489-95)
Intervention from the stage of pre-cachexia is best. Early nutritional intervention can improve nutritional status. This may reduce the inflammatory response. Stabilization of body weight during chemotherapy often results in reduced toxicity and longer overall survival. The following have all shown limited success.
Exercise is safe during active cancer treatments. It improves muscle strength, bone health, and quality of life, while decreasing depression, fatigue, and psychosocial distress. Physical activity can reduce the risk of comorbidities negatively affecting cancer survivors. There is evidence indicating that exercise is associated with a reduction in overall mortality. Physical exercise can improve insulin sensitivity, modulate muscle metabolism, and reduce the inflammation. Exercise has anti-inflammatory benefits. It up-regulates anti-inflammatory cytokines in skeletal muscle and adipose tissue. Recommendations should be made for exercise early in the treatment of cancer. Physical therapy evaluation can be helpful. Caregiver participation improves compliance.
Multiple agents with different mechanisms of action can be used alone or in combination.
Olanzapine, a selective monoaminergic antagonist, has a strong affinity for dopamine and serotonin receptors. It has been used at low doses showing improvement in weight and nutritional status with a low incidence of side effects.
Ghrelin and its analogs, including anamorelin have been shown to be effective. Side effects included nausea and hyperglycemia.
Recombinant-human GH with insulin has been evaluated and showed improved whole-body protein net balance.
Anabolic androgenic steroids have been used to promote muscle growth and strength. Nandrolone decanoate was studied in patients with non-small cell lung cancer. The treated group had less weight loss, but survival was comparable. Fluoxymesterone, an anabolic steroid, was found to be inferior to megestrol acetate or dexamethasone.
Enobosarm (GTx-024) is an androgen receptor modulator. It has tissue-selective anabolic effects in muscle and bone. One study showed an increase in lean body mass.
Thalidomide suppresses TNF production in patients with cancer. It has been used in combination with medroxyprogesterone or megestrol acetate, oral eicosapentaenoic acid, and L-carnitine resulting a significant increase in lean body mass significantly, decreased fatigue, and improved appetite.
MABp1 (Xilonix; Xbiotech, Inc., Austin, TX) is a fully humanized, monoclonal anti-IL-1a antibody. It is a receptor antagonist that resulted in partial remission or stabilization of cachexia.
Corticosteroids have been found in uncontrolled studies to diminish anorexia, asthenia, and pain in patients with cancer. The improvements did not persist, and all nutritional status returned to baseline with no differences in mortality rate.
Megestrol acetate has been used historically. It improves appetite and increases body fat more than lean body mass. There is a reduction of serum levels of IL-1a and b, IL-2, IL-6, and TNF-a.
Medroxyprogesterone acetate is a synthetic progestagen that also has been used. It reduces production of cytokines and serotonin. It has been to increase appetite but not weight.
Metoclopramide can be used for patients with delayed gastric emptying or gastroparesis.
Dronabinol and Marijuana Dronabinol (Delta 9-tetrahydrocannabinol, THC) have been studied. Cannabinoids have not shown to be more effective than megestrol despite improved appetite.
The anti-tnf antibody has been studied with conflicting results.
Eicosapentaenoic acid was found to have antitumor and anti-cachexia activities in animal cachexia models, but randomized clinical studies show no unique benefit of EPA.
Myostatin inhibitors may be a new potential therapeutic target. Activin type-2 receptor (ActRIIB) has been used to treat of muscle wasting. ActRIIB is a high-affinity activin type 2 receptor that is known to mediate the signaling via a subset of TGF-b family ligands including myostatin, activin, GDF11, and others.
Bimagrumab is a fully humanized anti-ActRII monoclonal antibody that is to be studied for non-small cell lung cancer associated cachexia.
NSAIDs including indomethacin and celecoxib have not been shown to improve nutritional status.
Hydrazine sulfate is an inhibitor of the enzyme phosphoenolpyruvate carboxykinase. It interrupts gluconeogenesis in animals. Studies have shown no benefit.
Beta-hydroxy-beta-methyl butyrate with L-arginine and L-glutamine has been used for cachexia. HMB is a metabolite of leucine and interferes with the activation of NF-kB. In tumor-bearing mice, it inhibited PIF-induced protein degradation and attenuated the increased protein degradation.
OHR/AVR118 (OHR Pharmaceuticals, Inc., New York, NY) is a broad-spectrum peptide-nucleic acid immunomodulator is theorized to have cytoprotective properties. A study in patients with cancer showed stabilization of body mass and muscle mass, increased appetite, and enhanced quality of life.
Total parenteral nutrition (TPN) has not been shown to have significant benefit for patients undergoing chemotherapy or radiation therapy regarding tolerance, response, or survival.
Cancer cachexia is a well-known problem for many patients with advanced malignancy. The cause of the cachexia is multifactorial and is best managed by a multidisciplinary team that consists of an oncologist, dietitian, social worker, pharmacist, physical therapist and a mental health counselor. The key is to recognize the problem early, when treatment is most successful. Even though there are many pharmacological agents that may help boost appetite, long-term studies on the effectiveness of these agents are lacking. At a minimum, the patient should be seen by a dietitian and a therapist. Improving the mood and offering supportive services may also help. Sadly, when cancer cachexia is advanced the outlook for most patients is poor and thus one should always try and ensure that the quality of life does not deteriorate.