New PET Approach Developed for Difficult Cancer Diagnosis

Researchers have developed a new imaging approach for identifying a rare form of thyroid cancer that is typically hard to diagnose. Accurate diagnosis of the cancer, known as poorly differentiated thyroid cancer (PDTC), can help clinicians choose the best treatment for the patient. The study results also raise the possibility of extending the use of radioiodine therapy to thyroid cancers where the thyroid gland cannot be surgically removed.

Radioiodine therapy takes advantage of the fact that thyroid cells are the only tissue that takes up iodine and thus delivers radioactive iodine to cancerous thyroid tissue. This targeted radiation therapy frequently is used to destroy any cancerous thyroid cells that remain after removal of the thyroid gland--an approach often used to treat thyroid cancer.

Malik Juweid, M.D., professor of radiology in the Roy J. and Lucille A. Carver College of Medicine at the University of Iowa (UI; Iowa City, USA), and colleagues used a compound called thyrotropin to stimulate radioactive iodine uptake by tumor cells in a patient who had cancer of unknown origin. Scanning was performed with a gamma camera. Fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging was done as an ancillary test supporting the radioiodine findings.

Concentration of radioiodine by the patient's tumor cells indicated that the thyroid was the primary site of patient's cancer and confirmed the diagnosis of PDTC. The stimulated radioiodine scan also showed that this patient's cancer cells did not take up enough radioactive iodine for this to be a good way to treat the tumor and thus a different treatment option, external beam radiation, was chosen. The investigators published their findings in the September 18, 2008, issue of the journal New England Journal of Medicine (NEJM). "Typically, radioiodine is used in two ways--as a scanning tool to visualize where thyroid tumor cells are in the patient and as a way to deliver radiation therapy to kill residual cancer cell after removal of the thyroid gland,” Dr. Juweid explained.

Although in this case the PDTC cells did not take up enough radioiodine to allow delivery of therapeutic doses of radiation, many PDTCs do take up large amounts of iodine. The study suggests that boosting uptake of radioiodine with thyrotropin might be a way to extend the use of radioiodine therapy to treat thyroid cancer even in cases where the thyroid gland cannot be surgically removed.

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