FDG PET detects thyroid cancer better than conventional imaging

October 03, 2001

Reston, VA... FDG PET detected recurrent cancer 50% more often than did conventional imaging in persons suffering from thyroid cancer who had indications that their cancer had recurred, according to results of a study published in the October issue of The Journal of Nuclear Medicine. As a result of the FDG PET scan, clinical management for almost 80% of the patients was changed.

The study looked at 37 persons with differentiated thyroid carcinoma (DTC) who had elevated levels of thyroglobulin and negative 131I whole-body scan results after a thyroidectomy and radioactive iodine treatment (the standard treatment for thyroid cancer). An elevated human thyroglobulin (hTg) level is an almost certain indicator that cancer persists or has recurred.

Some patients with metastases do not concentrate131I; and there are indications that these people are more likely to have more aggressive cancers. Finding a way to locate tumors when indications suggest recurrence but 131I scan results are negative is therefore particularly important.

Of the 37 patients who underwent PET scanning, 28 (76%) had positive findings. Conventional imaging of the same patients (Ultrasound, MRI, CT, and x-ray) gave positive results in only 10 cases (27%). For the ten patients in whom the conventional imaging did detect a tumor, FDG PET detected an additional 11 sites of disease, including distant metastases in 5 patients. For those whose cancer was only detected by the PET scan, there were 44 different tumor sites detected.

Overall, the PET scan findings changed the management of 29 patients. Twenty-three underwent surgery, and disease was confirmed for 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%.) Four patients, who were not candidates for surgery because of their disease's location, underwent external radiotherapy.

"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 131I posttherapy scan yet the patient's thyroglobulin levels are high," stated study coauthor Dr. Badia O. Helal.

FDG PET measures the body's metabolic activity. A patient undergoing PET scanning is injected with the radiopharmaceutical fluorodeoxyglucose (FDG) approximately 45 minutes before the scan. The radiopharmaceutical tracer emits signals that are picked up by the PET scanner. A computer reassembles the signals into images that display the distribution of metabolic activity as an anatomic image. Areas in which cancer is present will show up more brightly on the scan because the disease is more metabolically active than noncancerous cells.

Approximately 18,400 Americans are diagnosed each year with thyroid cancer, and approximately 1,200 people die annually from the disease. Papillary carcinoma and follicular carcinoma are the most common types of thyroid cancer and are often grouped together as DTC.

Thyroid cancer is considered one of the curable types of cancer and more than 90% of patients treated for DTC live for 15 years or longer after their initial diagnosis. There is, however, a 20% recurrence rate, and the prognosis for those patients depends on the ability to detect and treat the recurrence early.
Clinical Impact of FDG PET in Thyroid Carcinoma Patients with Elevated Thyroglobulin Levels and Negative 131I Scanning Results After Therapy" was written by Badia O. Helal, Pascal Merlet, Marie-Elisabeth Toubert, Brigitte Franc, Claire Schvartz, Hélène Gauthier-Koelesnikov, Alain Prigent, and André Syrota. Authors are located at Service de Médecine Nucléaire, Hôpital Antoine Béclère, AP-HP, Clamart; Départment de la Recherche Médicale, Service Hospitalier Frédéric Joliot, CEA, Orsay; Service de Médecine Nucléaire, Hôpital Saint-Louis, Paris; Service d'Anatomie Pathologie, Hôpital Ambroise Paré, Boulogne; Service de Médecine Nucléaire, Institut Jean-Godinot, Reims; and Service de Médecine Nucléaire, Hôpital Henri-Mondor, Créteil, France.

Copies of the article and images related to the study are available to media upon request to Karen Lubieniecki at Karenlub@aol.com, 703-683-0357. Copies of this and past issues of The Journal of Nuclear Medicine are available online at jnm.snmjournals.org. Print copies can be obtained at $15 per copy by contacting the SNM Service Center, Society of Nuclear Medicine, 1850 Samuel Morse Drive, Reston, VA 20190-5315; phone: 703-326-1186; fax: 703-708-9015; e-mail: servicecenter@snm.org. A yearly subscription to the journal is $170. A journal subscription is a member benefit of the Society of Nuclear Medicine.

The article is available online at http://jnm.snmjournals.org/cgi/content/full/42/10/1464?ijkey=HE6AfPoU1trUc&keytype=ref&siteid=snmjournals.

Society of Nuclear Medicine

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