Aim: The purpose of this prospective study was to investigate the role of 2-(fluorine-18)-fluoro-2-deoxy-D-glucose (18F-FDG) PET/computed tomography (CT) in the diagnosis of recurrent colorectal cancer (CRC) in patients with increased tumor markers and negative contrast-enhanced computed tomography (CeCT) results.
Material and methods: Forty-three patients (27 male; median age 66 years, range 31–93 years) with increasing tumor markers and negative CeCT during follow-up for treated CRC underwent 18F-FDG PET/CT examinations. The serum values of carcinoembryonic antigen (CEA) (n=29) and CA 19-9 (n=20) were normal after completion of treatment, with subsequent increasing concentrations.
Results: Among the 43 patients, 18F-FDG PET/CT was true positive in 32 (74.4%), false positive in two (4.7%), false negative in one (2.3%), and true negative in eight (1%) patients. On the patient-basis analysis, 18F-FDG PET/CT had a sensitivity of 97% (confidence interval: 0.82–0.99), a specificity of 80% (0.44–0.96), a positive predictive value of 94% (0.78–0.98), and a negative predictive value of 88% (0.5–0.99). There was no statistically significant correlation between CRC recurrence and CEA and CA19-9 levels (P=0.561 and 0.55, respectively). Only in the group of patients (n=6) with both tumor markers increased did 18F-FDG PET/CT have 100% accuracy in revealing recurrent disease.
Conclusion: 18F-FDG PET/CT is highly sensitive in the diagnosis of recurrent CRC in patients with increasing levels of tumor markers and negative CeCT regardless of the type or level of tumor marker; however, the combination of elevated CEA and CA 19-9 increases the likelihood of 18F-FDG in detecting recurrence.