Cambrosio et al. (2018. “Extending Experimentation: Oncology’s Fading Boundary Between Research and Care.” New Genetics and Society 37 (3): 207–226) argue that “experimental care” in contemporary oncology involves the rapid merging of patient research and care, and invite further study into developments across other health conditions. We present a 2018–2019 study of experimental breast cancer care in an urban clinical setting in the light of two other studies in the same hospital group: in the same cancer service (2013–14) and, prompted by these earlier findings, an interview study in HIV services (2014–15). We found that patients and staff anticipated better outcomes by treating sub-types of breast cancer but they also hoped for a better one-size-fits-all approach, akin to the antiretroviral treatments introduced for HIV and explored in our interview study. We conclude that the promise of targeted treatment for sub-types of disease – variously described as experimental care, personalised, precision, stratified and sub-group medicine – is accompanied by hopes for a single, standard, effective approach.