DETERMINE is an open-label phase II/III trial. It will look at targeted treatments in rare cancers or common cancers with rare genetic change (mutation). Participants must have a cancer with an identified mutation. This could be found during routine testing or as part of another research programme. The DETERMINE trial will recruit adults, teenagers and children. If a drug is found to benefit a new patient group, the study team will work with the NHS and the Cancer Drugs Funds to see if these drugs can be available for patients in the future.