Small animal PET in oncology: the road from bench to bedside

Positron emission tomography (PET) is routinely performed in patients with cancer for disease staging, assessment of relapse, and evaluation of therapy response. In addition to its well-established value in human malignant diseases, the use of special small animal PET (SA-PET) scanners have allowed for accurate assessment of small animals bearing human tumors. This application of PET provides whole-body, noninvasive, functional data of tumor lesions and can be used to assess abnormalities in the metabolic pathways of cancer, such as uncontrolled proliferation, increased apoptosis, and angiogenesis. Several positron-emitting tracers labeled with 18-fluorine and 11-carbon are currently available for PET studies to image abnormal biologic pathways of tumors. Moreover, SA-PET can be used to evaluate tumor-cell-receptor expression, a sign of tumor cells differentiation that is relevant for planning targeted therapies. Another advantage of SA-PET is the quantitation capability: Semiquantitation of the tumor activity can be performed at each scan and compared in the same animal over time to monitor tumor growth or to assess the response to new therapies. This review focuses on the applications of SA-PET for the visualization of the pathophysiologic pathways of tumor cells.