title: Value of CT, FDG PET-CT and serum tumor markers in staging recurrent colorectal cancer.
abstract: BACKGROUND
  Serum tumor markers and computed tomography (CT) are the most widely accepted monitoring tools for the follow-up patients with colorectal cancer (CRC). Positron emission tomography (PET) with 18[F]-fluorodeoxyglucose (FDG) is a promising modality for the evaluation of recurrent CRC. The purpose of this study was to (1) investigate the sensitivity and specificity of serum tumor marker assay, CT and FDG PET-CT, (2) determine the correlation of these markers with FDG PET-CT quantitative indices such as maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) in patients suspected to have recurrent CRC.
  
  
  METHODS
  FDG PET-CT imaging was performed in 212 patients with possible CRC recurrence. A retrospective study was performed on patients with (1) a history of CRC with complete remission after treatment, (2) pathology of adenocarcinoma and (3) increase in cancer antigen 19-9 (CA 19-9) and/or carcinoembryonic antigen (CEA) or suspicious radiological evaluation during follow-up after complete remission.
  
  
  METHODS
  All patients underwent integrated FDG PET-CT scan. Serum tumor markers were obtained within 3 months of PET-CT. All enrolled cases showed increase in a tumor marker over the reference value on at least two serial measurements or abnormal CT scan before PET-CT was performed. Results were compared with histopathological findings or clinical follow-up.
  
  
  RESULTS
  Following exclusion of 57 patients with missing data or lost to follow-up, 155 patients (87 men, mean age: 61 years) remained for final analysis. Serum CEA and CA 19-9 had a sensitivity of 74 and 35% and specificity of 86 and 83% for the detection recurrent CRC, respectively. The sensitivities of CT and FDG PET-CT were 79 and 92% and specificities were 45 and 100%, respectively. At an adaptive threshold of 42%, the median SUVmax, SUVmean, MTV and TLG of these lesions were 8.8, 5.2, 11.3 cm[Formula: see text] and 55.4, respectively. All FDG PET-CT quantitative parameters correlated positively with serum CEA levels, and the correlation coefficients were 0.45, 0.44 and 0.49 for SUVmax, MTV and TLG [Formula: see text].
  
  
  CONCLUSIONS
  PET-CT scan, CEA and CA-19-9 results were correlated. However, both tumor markers had poor sensitivity to detect metastatic disease. PET-CT is more accurate than CT in detecting recurrent CRC in this study. Majority of the recurrences were in the liver and the sensitivity is affected by tumor histology. The correlation between semiquantitative FDG PET parameters and serum tumor marker levels is moderate.
authors.affiliation: Department of Nuclear Medicine, Hacettepe University Medical Faculty, Siihiye, Ankara, 06100, Turkey, Mcaglart@gmail.com.
authors.forename: Meltem
authors.initials: M
authors.lastname: Caglar
authors.forename: Can
authors.initials: C
authors.lastname: Yener
authors.forename: Erdem
authors.initials: E
authors.lastname: Karabulut
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000097:blood*; D015179:Colorectal Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000175:diagnosis* / Q000000981:diagnostic imaging; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D019788:Fluorodeoxyglucose F18