• J. Nucl. Med. · Apr 2007

    Diagnostic accuracy of 18F-FDG PET in restaging patients with medullary thyroid carcinoma and elevated calcitonin levels.

    • Seng C Ong, Heiko Schöder, Snehal G Patel, Ida M Tabangay-Lim, Indukala Doddamane, Mithat Gönen, Ashok R Shaha, R Michael Tuttle, Jatin P Shah, and Steven M Larson.
    • Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
    • J. Nucl. Med. 2007 Apr 1; 48 (4): 501-7.

    UnlabelledMedullary thyroid carcinoma (MTC) is a rare endocrine tumor arising from the C-cells of the thyroid gland. Calcitonin is the principal serum tumor marker. A rising calcitonin level after total thyroidectomy for localized disease generally indicates residual, recurrent, or metastatic disease. The role of (18)F-FDG PET in MTC remains somewhat unclear. We reviewed our own experience with (18)F-FDG PET in postthyroidectomy MTC patients with elevated calcitonin.MethodsFrom our database, we identified patients with suspected residual, recurrent, or metastatic MTC and elevated calcitonin who had been referred for (18)F-FDG PET between January 2000 and October 2005. (18)F-FDG PET findings were classified as positive or negative on the basis of visual interpretation of the scan. Standardized uptake values (SUVs) were also calculated. The (18)F-FDG PET findings were verified by histopathologic examination, when available, or other imaging studies and clinical follow-up. Any negative (18)F-FDG PET result was considered false-negative.ResultsTwenty-eight patients underwent a total of 38 (18)F-FDG PET studies. Calcitonin levels ranged from 106 to 541,000 pg/mL (median, 7,260 pg/mL). There were 23 true-positive, 1 false-positive, and 14 false-negative (18)F-FDG PET scans, yielding an overall sensitivity of 62%. There was no true-positive finding when calcitonin levels were below 509 pg/mL (n = 5). Using an arbitrary cutoff of 1,000 pg/mL, we found that the sensitivity in scans with calcitonin levels greater than 1,000 pg/mL increased to 78% (21/27; 95% confidence interval, 58%-91%). The mean SUV of all lesions with (18)F-FDG uptake was 5.3 +/- 3.2 (range, 2.0-15.9). Among the 14 patients with false-negative (18)F-FDG PET findings, 8 had concurrent anatomic imaging studies and only 2 of these had positive findings.Conclusion(18)F-FDG PET can detect residual, recurrent, or metastatic MTC with a reasonable sensitivity of 78% when the calcitonin level is above 1,000 pg/mL but appears of limited use if the calcitonin level is below 500 pg/mL.

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