Positron Emission Tomography Imaging of Macrophages in Cancer

SIMPLE SUMMARY: Tumor-associated macrophages (TAMs) play numerous roles in cancer biology and are an important component of the relationship between immune system response and tumor progression. Several new immunotherapy techniques have been developed that target TAMs and are under investigation in both clinical and preclinical settings. Despite this surge of new immunotherapy techniques, a means to specifically and quantifiably measure the presence of TAMs to ensure the viability of these therapies, has yet to be widely investigated. The development of molecular imaging agents that target TAMs provides a path to noninvasively gain valuable insight into the molecular and functional characteristics of the tumor microenvironment and how the immune response facilitates the progression of cancer or therapy response. This article reviews published preclinical and clinical research in the imaging of TAMs through Positron Emission Tomography (PET). ABSTRACT: Macrophages are large phagocytic cells that can be classified as a type of white blood cell and may be either mobile or stationary in tissues. The presence of macrophages in essentially every major disease makes them attractive candidates to serve as therapeutic targets and diagnostic biomarkers. Macrophages that are found in the microenvironment of solid tumors are referred to as tumor-associated macrophages (TAMs) and have been shown to influence chemoresistance, immune regulation, tumor initiation and tumor growth. The imaging of TAMs through Positron Emission Tomography (PET) has the potential to provide valuable information on cancer biology, tumor progression, and response to therapy. This review will highlight the versatility of macrophage imaging in cancer through the use of PET.