DALLAS, March 29 -- When normal cells start to become cancerous, they develop an enormous appetite for glucose (the basic energy substrate of the body), says Michael Phelps, Ph.D., of the UCLA School of Medicine. After injection with a glucose analog tagged with fluorine-18, a radiotracer, a patient can be examined by a whole body PET scan to determine whether a tumor is malignant (high glucose metabolism) or benign, or whether the cancer has spread to any other organ systems of the body, he said here March 29 at a national meeting of the American Chemical Society, world's largest scientific society.
Such studies are being used to detect and stage the severity of cancer in patients with lung, breast, head and neck, colorectal, melanoma, lymphoma ovarian and prostate cancer. PET radiotracer techniques have also been used to identify the early metabolic alterations of degenerative diseases of the brain such as Alzheimer's, Parkinson's and Huntington's diseases. For example, at the early stage of disease when all other imaging techniques are normal, early metabolic alterations are readily apparent in PET scans and specific to each of the diseases, Phelps said. Further, studies of Huntington's disease and the genetic form of Alzheimer's have indicated that PET detects the metabolic abnormalities of these diseases prior to even the appearance of symptoms, as indicated by the genetic markers and long term follow up studies to identify patients that go on to have symptoms, he said.
Serial scans are used to follow the progressive spreading of the disease throughout an increasing number of structures within the brain, he explained. A similar approach is taken with Parkinson's disease, except fluorine-18 labeled L-DOPA is used to identify the early abnormalities of dopamine synthesis at a time of mild symptoms and normal structural imaging studies. PET is now being used to assess therapeutic interventions that would seek to stop or reverse the metabolic alterations on these degenerative diseases, according to Phelps.
On January 1, he said, the federal government began reimbursing physicians who used PET scans for diagnosing and staging the degree of metastasis in lung cancer. The government has also agreed to perform expedited reviews of 12 other clinical indications for PET. In addition, the Food, Drug and Cosmetic Act was changed this year in a bill sponsored by Senator Stevens, Chair of Appropriations, that directs the FDA to design a new review and regulatory approach that takes into account the special properties of PET, and that while this takes place, the US Pharmacopoeia will be employed as the legal standard of FDA approval, Phelps said. The USP has approved the radiotracers mentioned above for numerous diagnostic indications in cancer, heart disease and neurological diseases such as Alzheimer's, Parkinson's, stroke and epilepsy. Phelps points to this as evidence that advancement in radiotracer chemistry is allowing PET to move more fully in the everyday medical practice.
A nonprofit organization with a membership of more than 155,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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