Anorexia is an important issue in the management of elderly patients with cancer because it contributes to the development of malnutrition, increases morbidity and mortality, and negatively affects patients’ quality of life. This review summarizes the potential mechanisms of the development of anorexia in three animal models that mimic the situations commonly seen in elderly patients receiving chemotherapy. Cisplatin-induced anorexia is attributable to a decrease in peripheral and central ghrelin secretion caused by the stimulation of serotonin (5-hydroxytryptamine; 5-HT)_2B and 5-HT_2C receptors via 5-HT secretion. Age-associated anorexia is caused by an increase in plasma leptin, which results from disturbed reactivity of ghrelin in the hypothalamus and regulation of ghrelin secretion. Environmental change causes the activation of central 5-HT_1B and 5-HT_2C receptors and the melanocortin-4 receptor system, resulting in a decrease in circulating ghrelin levels which lowers food intake. New therapeutic approaches based on these pathophysiological mechanisms are warranted for the treatment of anorexia in cancer patients, especially elderly ones.