title: Diagnostic accuracy of 18F-FDG PET in restaging patients with medullary thyroid carcinoma and elevated calcitonin levels.
abstract: Medullary 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.
  
  
  METHODS
  From 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.
  
  
  RESULTS
  Twenty-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.
  
  
  CONCLUSIONS
  (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.
authors.affiliation: Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Seng C
authors.initials: SC
authors.lastname: Ong
authors.forename: Heiko
authors.initials: H
authors.lastname: Schöder
authors.forename: Snehal G
authors.initials: SG
authors.lastname: Patel
authors.forename: Ida M
authors.initials: IM
authors.lastname: Tabangay-Lim
authors.forename: Indukala
authors.initials: I
authors.lastname: Doddamane
authors.forename: Mithat
authors.initials: M
authors.lastname: Gönen
authors.forename: Ashok R
authors.initials: AR
authors.lastname: Shaha
authors.forename: R Michael
authors.initials: RM
authors.lastname: Tuttle
authors.forename: Jatin P
authors.initials: JP
authors.lastname: Shah
authors.forename: Steven M
authors.initials: SM
authors.lastname: Larson
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor; D002116:Calcitonin / Q000096:biosynthesis*; D018276:Carcinoma, Medullary / Q000175:diagnosis* / Q000378:metabolism*; D005189:False Positive Reactions; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging / Q000379:methods*; D012680:Sensitivity and Specificity; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000378:metabolism*
chemical_list: D014408:Biomarkers, Tumor; D019788:Fluorodeoxyglucose F18; D002116:Calcitonin