Because aging is highly individualized, the best guide to treatment of the older patient with cancer may be provided by a comprehensive assessment that evaluates such diverse areas as functional status, comorbidity, socioeconomic conditions, nutrition, polypharmacy, and the presence or absence of geriatric syndromes. Aging is further associated with important pharmacologic changes that involve pharmacokinetics, pharmacodynamics, and the toxicity profile of the drugs. These changes increase the risk of therapeutic complications partly because of the different behavior of the disease in an older patient population and partly because of a decreased tolerance to treatment in some older patients.