The growing incidence of cancer associated with an aging population implies major challenges for the care management of older adults with cancer. Several studies reported age as a limiting factor for access to cancer treatment, with older adults being less likely than younger patients to undergo surgery or receive anticancer drugs or radiation therapy. The main reason some treatments are not offered to older patients is to avoid overtreatment, i.e. to avoid either treatment of a cancer that would not have caused symptoms in the remaining lifetime, or treatment with serious adverse effects. These disparities are mainly based on higher risks of toxicity from anticancer drugs in older patients because of age-related comorbidities or vulnerabilities, which, when not based on objective evaluation, is a form of ageism. Indeed, being too cautious may lead to undertreatment with adverse consequences in terms of response to treatment or even survival. Poor representation of older patients in clinical trials is part of the explanation since high-quality evidence for treatment decisions is lacking. Older adults are often excluded from clinical trials, mainly on biological criteria or various tests rather than on valid criteria based on patient morbidities or vulnerabilities. Moreover, even when older patients are included, they are most often fit, and thus not representative of all older adults with cancer. Extrapolation of the results from studies on younger patients is not appropriate and more studies dedicated to older adults are therefore necessary, in particular with the aim of guiding therapeutic decisions.