Cancer Treatment Today

F-18 labeled fluorodeoxyglucose (FDG) is coming into increased being used as a scanning agent in positron emission tomography (PET), especially to diagnose and follow patients with different types of cancer, including thyroid.

There is supportive evidence for PET scan’s utility specifically for Hurthle cell type of thyroid cancer. Hurthle cell thyroid cancer is a differentiated thyroid cancer that is more similar to follicular than pappillary papillary thyroid cancer. Hurthle cell thyroid cancer tends to be more aggressive, metastasize more frequently, and trap iodine less avidly than follicular or papillary thyroid cancer. Sarkar and colleagues reviewed 9 patients with Hurthle cell cancer who had 12 PET scans and comparative 131-I scans. The 131-I scans were either performed while the patients were hypothyroid (10 studies) or while euthyroid, with the use of recombinant TSH (2 studies). The results showed that 4 patients had no discernible metastases on either 131-I or PET scans. The remaining 5 patients had a total of 8 FDG studies that showed metastases in the lungs, nodes, bone, and kidney. All the positive FDG scans were associated with elevated serum thyroglobulin concentrations. 131-I scanning was positive in only 1 case. In total, 131-I scanning missed metastases in 11 body regions. The authors concluded that in patients with Hurthle cell cancer, PET scans had greater diagnostic sensitivity than 131-I scanning.

There are several other studies that suggest the same conclusion more generally for thyroid cancer as a group.

• Sarkar S, Pugliese P, Palestro C. Metastases from Hurthle cell thyroid cancer are far more avid for fluorodeoxyglucose than for radioiodine. Program and abstracts of the 73rd Annual Meeting of the American Thyroid Association Meeting; November 7-10, 2001; Washington, DC. Abstract 53.
• Schluter B, Bohuslavizki KH, Beyer W, Plotkin M, Buchert R, Clausen M. Impact of FDG PET on patients with differentiated thyroid cancer who present with elevated thyroglobulin and negative 131I scan. J Nucl Med. 2001;42:71-76.
• Jadvar H, McDougall IR, Segall GM. Evaluation of suspected recurrent papillary thyroid carcinoma with fluorodeoxyglucose positron emission tomography. Nucl Med Commun. 1998;19:547-554.
• Wang W, Larson SM, Fazzari M, et al. Prognostic value of fluorodeoxyglucose positron emission tomographic scanning in patients with thyroid cancer. J Clin Endocrinol Metab. 2000;85:1107-1113.
• Hooft L, Hoekstra OS, Deville W. Diagnostic accuracy of 18-F-fluorodeoxyglucose positron emission tomography in the followup of papillary or follicular thyroid Cancer. J Clin Endocrinol Metab. 2001;86:3779-3786.