Fluorodeoxyglucose positron-emission tomography (FDG-PET) detected recurrent cancer 50% more often than did conventional imaging in people with thyroid cancer who had indications that their cancer had recurred, according to results of a study published in the October 2001 issue of the Journal of Nuclear Medicine. Indeed, use of the FDG-PET scan led to changes in clinical management in almost 80% of patients.
The study evaluated 37 persons with differentiated thyroid carcinoma, who had elevated levels of thyroglobulin and negative iodine(Drug information on iodine)-131 (I-131) whole-body scan results after a thyroidectomy and radioactive iodine treatment. An elevated human thyroglobulin (hTg) level is a strong indicator that the cancer persists or has recurred.
Some patients with metastases do not concentrate I-131, and there are indications that they are more likely to have aggressive disease. Finding a way to locate tumors when evidence suggests recurrence but I-131 scan results are negative is, therefore, particularly important.
PET Uncovers Additional Sites of Disease
Of the 37 patients who underwent FDG-PET scanning, 28 (76%) had positive findings. Conventional imaging of the same patients (ultrasound, magnetic resonance imaging [MRI], computed tomography [CT], and x-ray) produced positive results in only 10 cases (27%). Among the 10 patients in whom conventional imaging did not detect a tumor, FDG-PET detected an additional 11 sites of disease, including distant metastases in 5 patients. Among those whose cancer was only detected by the PET scan, 44 different tumor sites were detected.
Overall, the FDG-PET scan findings changed the management of 29 patients; 23 underwent surgery, and disease was confirmed in 20. In three patients, pathology determined that the high FDG uptake was the result of inflammatory disease, for an overall true-positive rate of 70%.
"Our study shows that PET detects significantly more disease than conventional images for these cancer patients. We believe that a PET scan should be added as a first-line investigative tool to look for disease when there is a negative I-131 posttherapy scan yet the patient’s thyroglobulin levels are high," said study coauthor Dr. Badia O. Helal, Hôpital Antoine Béclère, Clamart, France.