Cancer imaging involves the use of molecular imaging technology to accurately diagnose, manage and treat many types of cancer.
Cancer imaging, or tumor imaging, allows physicians to:
Identify Tumor Properties and Growth
Tumor imaging allows physicians to accurately characterize a tumor's biological properties and to select the treatment most likely to be effective based on the tumor's characteristics.
Molecular imaging can provide much quicker information about treatment effectiveness. For example, a PET Scan allows physicians to see within days of treatment how the tumor was affected by the therapy. CT scans can only show if cancer cells are still active by waiting for an increase in size, which shows up months later.
Treat the Tumor
Through radioimmunotherapy, physicians can deliver concentrated, cell-killing doses of radiation directly to the tumor, decreasing radiation exposure to healthy tissue.
Click on the image to view the report on the "Clinical Utility of PET in a Variety of Tumor Types" from the Journal of the National Comprehensive Cancer Network.
Molecular imaging (MI) has made a significant impact on the field of oncology and is playing an increasingly important role in the diagnosis and treatment of cancer, through clinical applications, research and drug development. MI has become part of standard care for many types of cancer. MI allows physicians to accurately characterize tumor or biological processes, extent, location, response to treatment and prognosis. Molecular imaging is also increasingly being used for therapy, providing a means of target-specific drug delivery.
Molecular imaging helps determine the location, extent and metabolic activity of the disease.
Molecular imaging provides information for better decision-making with regard to chemotherapy (continue, abandon or change) surgery (biopsy, attempt surgical resection, abort planned resection) and radiotherapy (defining radiation therapy port boundaries, palliation or attempted cure).
PET scans provide an early and accurate way to determine if cancer is responding to treatment. In addition to enabling changes in patient management to be made in real time, it also helps predict treatment response before therapy is initiated.
Molecular radiotherapy (MRT) is a systemically administered, targeted therapy that delivers radiation at the cellular and molecular level. In contrast to chemotherapy, wherein all proliferating cells are affected, MRT delivers radiation to only those cells that express cancer markers.
The prototypical example of molecular radiotherapy is radioiodine treatment of thyroid cancer. MRT is also used to treat indolent non-Hodgkin’s lymphoma, using two FDA-approved, antibody-based molecular radiotherapeutics: Bexxar® or Zevalin®.
Radiolabeled peptides have shown to be beneficial in the treatment of neuroendocrine tumors. Unlike the therapeutic regimens of Bexxar and Zevalin which are based on intact antibodies, peptides are typically made up of fewer than 50 amino acids. 111In-DTPA-octreotide (Octreoscan), was approved by the FDA in 1994 for imaging/detection of neuroendocrine tumors with somatostatin receptors based on trials conducted exclusively outside the of the United States.
Both promising new antibody-based and peptide-based MRTs continue to be developed and comparative trials will be needed to determine how these will be used with current treatment against neuroendocrine tumors.
Metaiodobenzylguanidine (MIBG) is an aralkylguanidine analog of catecholamine precursors, structurally similar to norepinephrine that concentrates within secretory granules of catecholamine producing cells. It has been labeled with 123I for diagnostic imaging and with 131I for therapy of neuroblastoma, pheochromocytoma, and, to a lesser extent, other neuroendocrine tumors.
Molecular imaging technologies used in oncology include:
FDG is not only a cancer-specific imaging agent, false positive results may be observed with benign diseases. False positive results are commonly observed in areas of active inflammation or infection, with a reported false positive rate of approximately 13 percent and false negative rate of approximately 9 percent. Accumulation of FDG only indicates enhanced cellular metabolism, irrespective of the nature of the cells. Areas of activated macrophages as well as metabolically active carcinomas will all accumulate FDG. Due to the limited specificity of FDG-PET/CT in excluding malignancy, FDG positive lymph nodes and metabolically active masses require histologic assessment to avoid incorrect diagnosis and potentially limiting treatment options for patients. The absences of FDG accumulation in lesions and lymph nodes is highly predictive for the absence of active disease, but false negative results can also be observed in malignancies with low metabolic activities.1
1Carter K, et al “Common Causes of False Positive F18 FDG PET/CT Scans in Oncology” Brazilian Archives of Biology and Technology 2007; 50: 29-35, September 2007–.
Nuclear medicine uses very small amounts of radioactive materials to diagnose and treat disease. The radiation risk involved in these procedures is very low compared with the potential benefits.
Medicare and Medicaid cover PET-CT studies for many but not all cancers. Major insurance companies and health maintenance organizations also provide coverage for PET-CT studies for cancer. Patients should check with their own insurance company for specific information on their health plan’s coverage and payment policies.
Patients being treated for a cancer that is not currently covered by insurance may be eligible for reimbursement by participating in the National Oncologic PET Registry (NOPR). Information collected in this database will help the Centers for Medicare and Medicaid Services (CMS) determine whether PET scans should be covered for other types of cancer, in addition to those that are currently reimbursable under Medicare.
Molecular imaging plays an important role in research into the causes and treatments of cancer by helping to:
Molecular imaging and therapy are on the forefront of the trend toward personalized cancer treatment. The goal is to be able to accurately assess variables (variations in pharmacokinetics in whole body, organs and tumors; varying receptor statuses and proliferative/apoptotic rates in tumors;) and to individualize treatments to optimize response and minimize toxicity.
Increasingly, MI is able to assist practitioners in:
Molecular imaging will likely become established as a tool for measuring biomarkers, or indicators of disease or therapeutic effects. Trials using a variety of molecular imaging techniques to validate this function are underway.
Potential uses of molecular imaging biomarkers include:
The potential benefits of imaging biomarkers in clinical trials include:
As the fields of molecular biology and genomics advance, tumor properties and pathways will be revealed, leading to a set of new cancer specific targets. Molecular radiotherapies can be developed to target tumor cells based on these advances.
Cancer cells have unique properties that can be exploited by nanoparticles. Guided by and/or in conjunction with molecular imaging technologies, nanoparticles can be targeted at cancer cells to:
Other advancements include:
Other probes are being developed to measure the early effects of cancer gene expression, including the differential or aberrant expression of:
Technologies under development include: