Molecular imaging of tumor microenvironment: challenges and perspectives

Tumor microenvironment consists of a number of components including host resident stromal cells, infiltrating immune cells and extracellular matrix. The architecture surrounding tumor cells is not static but is subjected to a continuous remodeling in response to the dynamic interplay between tumor and stromal cells and to the production of extracellular proteases. In addition all these microenvironmental components along with cancer cells are exposed to abnormal physiologic conditions such as hypoxia and acidic extracellular pH that may induce both adaptive and constitutive changes in cancer and stromal cells. In this review, we will primarily focus on the possibility to visualize in vivo tumor microenvironment components and conditions as well as interactions with cancer cells. The major goal is to highlight the difficulties and the opportunities of this approach and how each imaging technology helps to overcome specific challenge.