Tumor growth is associated with profound metabolic and neurochemical alterations, which can lead to the onset of anorexia-cachexia syndrome. Anorexia is defined as the loss of the desire to eat, while cachexia results from progressive wasting of skeletal muscle mass--and to a lesser extent adipose tissue--occurring even before weight loss becomes apparent. Cancer anorexia-cachexia syndrome is highly prevalent among cancer patients, has a large impact on morbidity and mortality, and impinges on patient quality of life. However, its clinical relevance is frequently overlooked, and treatments are usually only attempted during advanced stages of the disease. The pathogenic mechanisms of cachexia and anorexia are multifactorial, but cytokines and tumor-derived factors have a significant role, thereby representing a suitable therapeutic target. Energy expenditure in anorexia is frequently increased while energy intake is decreased, which further exacerbates the progressive deterioration of nutritional status. The optimal therapeutic approach to anorectic-cachectic cancer patients should be based on both changes in dietary habits, achieved via nutritional counseling; and drug therapy, aimed at interfering with cytokine expression or activity. Our improved understanding of the influence a tumor has on the host's metabolism is advancing new therapeutic approaches, which are likely to result in better preservation of nutritional status if started concurrently with specific antineoplastic treatment.