Anorexia is a lack of appetite that results in significant weight loss. There are a number of causes of anorexia associated with cancer. One cause is related to substances released by cancer tumours, such as pro-inflammatory cytokines, lactate, and parathormone-related peptide; by tumours causing dysphagia or altering gut function; by tumours which alter nutrients, such as zinc deficiency; by tumours causing hypoxia (low levels of oxygen in the tissues); by increased levels of serotonin; or by alterations of hormones that affect appetite.

Anorexia can also be caused by depression and pain, both of which can decrease the desire to eat. Within the central nervous system, tumours create multiple alterations in neurotransmitters, neuropeptides, and prostaglandins, all of which modulate eating and appetite.[1] Approximately 15-25% of patients are suffering from anorexia at diagnosis, but it can also be a result of treatments or the tumour itself. Radiation and chemotherapy can also worsen the initial effects of the tumour by altering the taste and smell of foods as well as causing nausea and vomiting.

Anorexia can lead to cachexia, which is a progressive wasting disease marked by the loss of fat and muscle. Sarcopenia is a condition where there is severe muscle depletion. About 50% of patients with advanced cancer suffer from sarcopenic obesity, which means that they are in a chronic low-level inflammatory state where the body loses muscle and gains fat. This is associated with increased toxicity of treatment, and therefore treatment interruptions and dose reductions may help. Nutritional interventions can improve outcomes by helping patients maintain weight staying on the intended treatment regimen with fewer changes, improving quality of life, and producing better surgical outcomes.[2]