FDG-PET Detects Thyroid Cancer Better Than Conventional Imaging

December 1, 2001

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

Fluorodeoxyglucose positron-emission tomography (FDG-PET)detected recurrent cancer 50% more often than did conventional imaging in peoplewith 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 inclinical management in almost 80% of patients.

The study evaluated 37 persons with differentiated thyroid carcinoma, who hadelevated levels of thyroglobulin and negative iodine-131 (I-131) whole-body scanresults after a thyroidectomy and radioactive iodine treatment. An elevatedhuman thyroglobulin (hTg) level is a strong indicator that the cancer persistsor has recurred.

Some patients with metastases do not concentrate I-131, and there areindications that they are more likely to have aggressive disease. Finding a wayto locate tumors when evidence suggests recurrence but I-131 scan results arenegative is, therefore, particularly important.

PET Uncovers Additional Sites of Disease

Of the 37 patients who underwent FDG-PET scanning, 28 (76%) had positivefindings. Conventional imaging of the same patients (ultrasound, magneticresonance imaging [MRI], computed tomography [CT], and x-ray) produced positiveresults in only 10 cases (27%). Among the 10 patients in whom conventionalimaging did not detect a tumor, FDG-PET detected an additional 11 sites ofdisease, including distant metastases in 5 patients. Among those whose cancerwas only detected by the PET scan, 44 different tumor sites were detected.

Overall, the FDG-PET scan findings changed the management of 29 patients; 23underwent surgery, and disease was confirmed in 20. In three patients, pathologydetermined that the high FDG uptake was the result of inflammatory disease, foran overall true-positive rate of 70%.

"Our study shows that PET detects significantly more disease thanconventional images for these cancer patients. We believe that a PET scan shouldbe added as a first-line investigative tool to look for disease when there is anegative I-131 posttherapy scan yet the patient’s thyroglobulin levels arehigh," said study coauthor Dr. Badia O. Helal, Hôpital Antoine Béclère,Clamart, France.