Cancer is a disease of the elderly. Cancer incidence is 11-fold higher in persons over the age of 65, than in younger ones. Approximately 60% of all cancers and 70% of cancer mortality occurs in people older than 65 years. Moreover, due to the aging of the population in the Western world the number of elderly people is expected to increase and therefore the number of older cancer patients is expected to rise. Despite this rapid increase in cancer incidence and cancer-related mortality with age, our knowledge about ageing and cancer and about optimal treatment for older cancer patients is still far from adequate. Therefore, it is clear that cancer in the elderly is a major and increasing health problem. A key problem in geriatric oncology research is the important selection bias because very old/frail patients, are very rarely included in clinical trials.