Our hypothesis is that with 18F-FDG PET, performed routinely in the initial assessment in elderly patients with cancer, it is also possible to obtain reliable and objective parameters of brain function and frailty. 18F-FDG PET is already used to identify cognitive and thymic impairment. This exam would help to assess the frailty and to adapt as best oncologic treatments some of which can also be neurotoxic. 18F-FDG PET is therefore related to brain function in frail patients