Research and care have been variably entangled in the UK health system. In the 1980s, internal – and other – markets were introduced into the National Health Service, which contributed to the demarcation of clinical research and standard care. During the last twenty years, however, developments in -omics associated with precision medicine have emphasised the necessary interplay between research and other clinical practice, commonly associated with experimental medicine. In the midst of this experimental phase, patients are also research participants and they experience many uncertainties about who is treating them for what, in which order, to what end. These problems are exacerbated by the government’s austerity programme, as I show with reference to breast cancer services in a London hospital group. I examine continuities between experimental care for breast cancer and earlier services for another health condition. From this perspective, precision medicine arose out of a failure of treatment. But healthcare staff and researchers anticipate a turn away from personalised towards sub-group medicine and, in the absence of new blockbuster drugs, the pharmaceutical industry is pursuing related strategies of market segmentation. However, the categories that are likely to emerge will differ from previous forms of social and medical stratification since the large, linked datasets through which an individual is classified ‘precisely’ will render her a partial and provisional member of many groups at once, which will constantly change as they are updated.