Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels. Angiogenesis is a normal and vital process in growth and development, as well as in wound healing and during the menstrual cycle. However, it is also a fundamental step in the transition of tumors from an inactive state to a malignant one.
In normal physiological condition, angiogenesis is well controlled by pro- and anti-angiogenic factors. In cancer, when the balance between both is disturbed, tumor cells secret a number of pro-angiogenic factors that stimulate the proliferation and migration of endothelial cells, resulting in the outgrowth of new capillaries into the tumor tissues for oxygen and nutrition supply and later on as path for metastasis.
So far the “gold standard” of quantifying tumor angiogenesis is Microvessel Density (MVD), an immune-histochemical staining technique applied to excised tumor. Advanced imaging techniques that provides microvascular and hemodynamic properties of tumor stand out against MVD due to its non-invasiveness, capability of evaluating the whole tumor and being repeated frequently during the treatment course.
Among these imaging techniques developed to evaluate the microcirculation, the analysis of the tissue kinetics of intravenously injected contrast agents is widely used. It encompasses enhancement for CT, ultrasound and dynamic contrast-enhanced MRI.
Today there are more and more novel therapeutic agents targeting the microvascular blood supply of a tumor. Many targeted therapeutic agents treat cancer by inhibiting angiogenic processes or disrupting the available vessels of tumor through altering single or multiple signaling pathways. In such treatment settings assessing the change of angiogenic status of cancer during the treatment course is becoming a part of oncologic practice in modern hospitals.