Diagnosis and follow-up in clinical oncology are traditionally based on computed tomography (CT). In recent years, however, functional imaging using positron emission tomography (PET) has been recognized as an important imaging modality and adjunct to CT that provides complementary metabolic information in many oncology applications. To overcome the challenges of aligning independently acquired PET and CT image sets several ad hoc concepts of integrating PET and CT imaging in a single device have been proposed. This article comments on the development of the first combined dual-modality PET/CT prototype at the University of Pittsburgh, and illustrates commercial advances to dual-modality PET/CT tomography. The current PET/CT designs from the major manufacturers comprise a commercial CT scanner in tandem with a commercial PET scanner. While the level of physical integration is actually less than that of the original prototype it is fair to assume that current PET/CT models may serve as intermediate solutions towards near-future design concepts that aim at greatly reduced costs of the dual-modality tomographs and offer a greater level of physical integration. The goal of the next generation of PET/CT systems is to design and build a device specifically for imaging the function and anatomy of cancer in the most informative and effective way without necessarily conceptualizing it as combined PET and CT scanners. Such a concept of a diagnostic imaging device relates more to a disease management approach rather than the usual division into medical specialities such as radiology and nuclear medicine.