| Abstract: |
Cancer is a complex series of stepwise genetic alterations resulting in common biologic changes in the transformed cells. Distinguishing features of cancer include rapid proliferation of cells, immortality, resistance to apoptosis, resistance to suppression of proliferation, metastatic behavior, characteristic changes in metabolism, and resistance to immunologic attack. Cancer cells recruit normal host tissues to support growth of the tumor mass. Fibrocytes and collagen producing cells provide structure for the tumor cells. Endothelial cells are recruited to form blood vessels. Tumor blood vessels have incomplete endothelium, making the vessels leaky. This allows large molecules to leak into the tumor interstitium. The middle of the tumor mass has few, if any, lymphatic vessels. The combination of vessel leakiness and few lymphatics results in an increased interstitial pressure in the tumor, making it difficult for chemotherapy to diffuse into the tumor mass. A common anatomic approach to measure tumor response (RECIST) employs measurements of the size of the mass on CT before and 4 weeks after therapy. Total disappearance of the lesion is required for a complete response, a 30% reduction in the sum of long dimensions defines a partial response, and>20%increase in the sum of long diameters identifies progressive disease. Adding metabolic information recorded with [18F]FDG-PET/CT and the PERCIST criteria may refine these measurements. In addition to [18F]FDG, radiopharmaceuticals are available to measure other attributes of the tumor. Depending on the radiopharmaceutical, images can provide information on tumor hypoxia, expression of integrins, or specific tumor markers that are overexpressed by the lesion, such as carbonic anhydrase, expressed by renal cell cancer, or receptors, such as somatostatin, expressed on neuroendocrine tumors. © Springer International Publishing Switzerland 2017. All rights reserved. |
