The aim of our study was to evaluate the accuracy of 18F FDG positron emission tomography/computed tomography (PET/CT) in assessing the presence of recurrent colorectal cancer, in relation to carcinoembryonic antigen (CEA) and Carboidrate antigen 19.9 (CA 19.9).
18F FDG PET/CT was performed in 72 patients for re-staging colon cancer. Therapy has been discontinued at least three months before the examination. The mean CEA value (measured in 64 patients prior PET/CT examination) was 31.15 (±128.3) whereas the CA 19.9 (measured in 64 patients prior PET/CT examination) were 67.5 (±173.3). Differences in CEA and CA 19.9 values in patients with a positive and negative scans were analysed by means of ROC curve. ROC curve has been used for the calculation of sensitivity and specificity of 18F FDG PET/CT for CEA and CA 19.9 levels.
Results of 18F FDG PET/CT were related to CEA levels and CA19.9. PET/CT was positive for recurrence in 45/74 patients (60.8%, mean CEA and CA 19.9 were, respectively 40.97 ± 159.7 and 81.81 ± 212.3); PET/CT was negative for recurrence in 29/74 patients (39.2%, mean CEA and CA 19.9 were, ,respectively, 14.79 ± 37.29 and 43.99 ± 73.46). As expected, CEA values were higher in patients with a positive scan as compared to negative scans (p=0.027). A CEA value lower than or equal to 3.8 ng/ml was associated with a positive scan in 7/27 subjects while 31/39 subjects with a CEA cut-off value greater than or equal to 3.8 ng/ml were positive for recurrence at PET/CT (p= 0.029; sensitivity 70%; specificity 70.9%).To note that CEA values were available in 66 subjects. We did not find statistically significant differences when comparing CA19.9 levels in patients with a positive or negative scan respectively.
The possibility of detecting recurrence in patients treated for colorectal cancer with 18F FDG PET/CT is related to CEA and not to CA 19.9 serum levels. In particular, during follow up, 18F FDG PET/CT should be recommended in patients with a CEA value of at least 3.8 ng/ml.