What is appetite loss? How does it affect cancer patients?

Related conditions:
Cachexia

Definition:
Loss of appetite in cancer patients, referred to by medical professionals
as anorexia, may result from either the cancer itself or the treatments used to
combat the disease. Cancer-related anorexia is associated with weight loss and has
been shown to correlate with a poorer outcome and a lower quality of life.

Risk factors: Those with cancer and undergoing chemotherapy
for cancer are at risk.

Etiology and the disease process: Because many cancer treatments
affect not only cancer cells but also healthy cells, several unwanted side effects
may result. For instance, chemotherapy may reduce the turnover of taste receptor
cells in the tongue, which may alter the flavor of food. Additional damage to
other cell types in the mouth may result in sores, gum disease, dry mouth,
and sore throat. Cells in the digestive tract may also be injured, resulting in
abnormal gut motility and difficulty swallowing. Together, these effects may
change the way food tastes and decrease the desire to eat.

Emotional side effects, such as fear and depression,
as well as psychological effects, such as the development of taste
aversions due to the nauseating side effects of chemotherapy,
can also contribute to the loss of appetite. Furthermore, many cancer patients
with anorexia report early satiety, meaning that they feel full after eating only
a small amount of food.

Biological causes for cancer-related anorexia also exist. Cytokines
released by tumor cells or produced by immune cells in response to cancer may
affect the central nervous system and the gastrointestinal tract to promote
appetite loss. Specifically, the central nervous system is responsible for
controlling food intake and energy homeostasis, while effects on the
gastrointestinal tract can influence feelings of fullness. Examples of cytokines
that may affect appetite include tumor necrosis factor-alpha (TNF-α), C-reactive
protein, interleukin-1 beta (IL-1 beta), IL-6, and tumor-derived lipid mobilizing
factor (LMF). However, there is some conflicting data as to whether blood levels
of these cytokines correlate with, or are responsible for, the loss of
appetite.

Incidence: In general, approximately 25 percent of cancer patients report loss of appetite. The incidence can be as high as 90 percent for patients with advanced cancers. However, different types of cancers tend to have different rates of anorexia. For example, approximately 60 to 80 percent of patients with cancers of the lung, stomach, pancreas, or esophagus have significant weight loss caused, in part, by anorexia. However, loss of appetite is not as frequent in patients with breast or prostate cancer.

Treatment and therapy: Cancer-related anorexia may be managed by either changing eating habits or taking medication. There are several dietary suggestions for cancer patients who struggle with loss of appetite. Liquid or powdered meal replacements as well as juice, soups, and milk-based drinks or shakes may be used in place of solid food to provide nutrients. Eating several small meals or snacks instead of three large meals per day may also be more feasible for patients with cancer-related anorexia. Additionally, drinking a glass of wine or exercising regularly may also stimulate the appetite. However, patients should consult with their doctors before consuming alcohol or beginning an exercise regimen.

The pharmacological treatment of cancer-related anorexia can be broadly divided into three groups: appetite stimulants, anticatabolic agents, and anabolic agents.

Examples of appetite stimulants include progestational agents (such as megestrol
acetate and medroxyprogesterone), which can improve caloric intake.
Corticosteroids (such as prednisolone and
methylprednisolone) may improve appetite because of their inhibition of
prostaglandin metabolism and IL-1 signaling. Cyproheptadine, an antihistamine, is
also a serotonin antagonist, and its effects on this neurotransmitter in the brain
can also promote an increase in appetite. A more controversial appetite stimulant
is cannabis (marijuana), as it can stimulate CB1 receptors in the brain
to enhance appetite and can also reduce nausea and cancer pain.

Anticatabolic agents, which inhibit the production or activity of appetite-decreasing cytokines, are also important in combating cancer-related anorexia. Examples include thalidomide (a potent inhibitor of TNF-α production) and eicosapentaenoic acid (an inhibitor of adenylate cyclase activity and tumor-derived LMF activity).

Anabolic agents such as oxandrolone and fluoxymesterone have been studied as well, and they may build lean tissue mass by increasing muscle protein synthesis. The hormone androgen may also be useful in cancer patients (except for those with hormone-dependent tumors) as it can promote muscle growth and strength and may also induce the secretion of leptin, a hormone produced by adipose tissue to stimulate appetite.

Prognosis, prevention, and outcomes: Generally appetite loss resolves
itself when its underlying cause is remedied. Although appetite loss can interfere
with the healing process, it does not usually increase mortality in patients with
early-stage cancers. However, cancer-related anorexia is often associated with
cachexia, a wasting syndrome characterized by not only the
loss of appetite but also weight loss, breakdown of muscle tissues, depletion of
reserves within fat (adipose) tissue, fatigue, and weakness. In advanced-stage
cancer, the cancer anorexia-cachexia syndrome is observed in about 80 percent of
patients and is one of the most frequent causes of death.

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