UICC World Cancer Congress 2006

Radiologic images have been used for decades to gauge the effectiveness of various therapeutic interventions. In the areas of oncology, cardiovascular disease, neurology, arthritis and osteoporosis, imaging plays a vital role determining the effectiveness of therapy for an individual patient. Increasingly, imaging also is being utilized during all phases of therapeutic drug development, resulting in speedier drug discovery and, in some instances, ensuring a drug's safety.

There has been an “explosion” in use of biomarkers in patient care as well as in drug discovery. Many imaging biomarkers are already commonly used, such as tumor size measured at CT to reflect tumor burden; T2 hyperintensity detected at brain MR imaging to reflect the burden of multiple sclerosis; and bone density determined with DEXA studies to assess for osteoporosis. One major benefit of imaging biomarkers is that the findings may be evaluated and quantified for changes over time. Newer imaging biomarkers are also playing a role in drug discovery, such as dynamic contrast-enhanced MR imaging to assess for vascular flow to tumors; molecular imaging in the functional evaluation of cardiac, neurologic and oncologic processes; and CT scoring systems in the evaluation of cystic fibrosis. The complexity in imaging biomarkers is increasing not only with the number of available imaging and post-processing techniques, but perhaps even more importantly, with the number and diversity of relevant therapeutic options. Increasingly, it is becoming clear that a single imaging biomarker alone can be misleading, but is more robust when combined with other imaging or non-imaging biomarkers. For instance, what is the significance of a gastrointestinal stromal tumor that remains unchanged in size at CT but whose SUV at PET has decreased, or of increased radiotracer uptake on a bone scan when the PSA value is declining?

Ultimately, the goal of imaging is to serve as a successful surrogate endpoint for a patient's response to therapy. Thus, tumor shrinkage as measured at CT should correlate with prolonged survival and an increase in bone density as measured by DEXA should correlate with decreased fracture rate -- analogous to how another commonly used biomarker, blood pressure, correlates with a decreased incidence of stroke in patients on antihypertensive therapy. Correlating and validating biomarkers is quite controversial (such as the conflicting recommendations of the WHO and the RECIST criteria for tumor measurement), greatly debated, and undergoing intense research.