Seeing and Believing: Medical Isotopes in Functional Cancer Imaging

The personalized-medicine revolution has started. Cancer is a highly heterogeneous group of disorders, and the current classification based on the organ of origin may only provide an incomplete picture of the biological behaviour of a cancer. Furthermore, there is increasing evidence that tumors are heterogeneous even in the same patient: as the cancer progresses and metastasizes, mutations can and do occur. Technologies such as positron emission (PET) go beyond the simple imaging of tumor location and size to allow visualization of physiological and biochemical processes in vivo. With the explosion of new predictive and prognostic biomarkers, new methods to develop targeted agents through combinatorial libraries and advances in radiolabeling techniques, PET imaging offers a unique window on the biology of cancers affecting patients.

In oncology, PET  imaging currently plays an important role in detecting the extent of malignant involvement (staging), as well as assessing the response of cancers to therapy. This is currently done using a glucose analog, 18F-Fluorodeoxyglucose, developed over 35 years ago. However, PET imaging can go far beyond imaging glucose metabolism. Hybrid imaging instruments combining PET and computed tomography (PET/CT) now integrate anatomical with molecular imaging in a single examination. A new generation of hybrid devices incorporating PET and magnetic resonance imaging (PET/MRI) offers the promise to combine the molecular imaging capabilities of PET with the tissue characterization capabilities of MRI.

The field is also growing rapidly with the identification of several new targets for imaging with radiolabeled probes. This includes imaging new blood vessel formation, cell division, and even the presence of specific molecules such as hormone receptors. These capabilities are rapidly expanding with the advent of new medical isotopes and new biologically specific molecules.

This presentation will provide some current examples of the clinical utility of positron emitting radioisotopes in oncology, and will review new advances that highlight how radioisotopes combined with targeted molecules can characterize cancers in vivo, without the need for biopsies.