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Researchers from the U.K. have reported that imaging with a combination of positron emission tomography (PET) and computed tomography (CT) can detect recurrent or metastatic thyroid cancer in patients who have an elevated thyroglobulin level and a negative (131)I whole-body scintigraphy examination (WBS). These results were published in the Journal of Nuclear Medicine.

Patients with thyroid cancer are often treated with total thyroidectomy followed by radio-iodine ablation. After treatment, measurement of thyroglobulin levels and (131)I whole-body scintigraphy examination may be used to monitor patients for cancer recurrence.

To explore the role of a combined PET/CT scan in detecting recurrent thyroid cancer, researchers conducted a study among 61 patients who had been treated for thyroid cancer. Patients were eligible for the study if they had elevated thyroglobulin levels or another reason to suspect the presence of recurrent cancer. Fifty-nine of the 61 study participants had negative WBS results.

A CT scan uses computer-controlled X-rays to create a three-dimensional image that helps the physician estimate the extent of the disease. A PET scan is another imaging technique. Prior to a PET scan, a substance containing a type of sugar attached to a radioactive isotope (a molecule that spontaneously emits radiation) is injected into the patient’s vein. The cancer cells “take up” the sugar and attached isotope. The low energy radiation emitted by these cells helps physicians locate cancer.

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  • Overall, PET/CT detected 68% of recurrent cancers. The ability of PET/CT to detect recurrent cancer did not vary by thyroglobulin level.
  • Among patients without a cancer recurrence, PET/CT correctly classified 82% as negative.
  • A second primary (a new thyroid cancer) was identified in two patients.
  • Clinical management changed for 27 of 61 patients based on PET/CT findings.

This study suggests that PET/CT may be useful in the diagnosis and management of selected patients suspected of having recurrent thyroid cancer.

Reference: Shammas A, Degirmenci B, Mountz JM, et al. 18F-FDG PET/CT in patients with suspected recurrent or metastatic well-differentiated thyroid cancer. Journal of Nuclear Medicine. 2007;48:221-226.

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