Cancer therapy has taken a major leap forward in recent years. However, to fully unfold the concept of precision medicine, non-invasive methods for characterisation of tumours and metastases are needed. PET imaging offers this. Whereas 18F-fluorodeoxyglucose-PET is currently used in most cancer types for diagnosing or staging, we expect new tracers to become available in the clinical routine, supporting tailoring and monitoring of cancer therapies.