The role of FDG-PET/CT in the detection of recurrent colorectal cancer

The conventional diagnostic techniques used to assess recurrence of colorectal cancer (CRCR) often yield unspecific findings. Integrated FDG-PET/CT seems to offer promise for the differential diagnosis of benign and malignant lesions. The aim of this study was to compare the value of FDG-PET and PET/CT in the detection of CRCR subsequent to colonic resection or rectal amputation.

The population for this retrospective study comprised 84 patients with suspected CRCR. The sensitivity, specificity and accuracy of PET and PET/CT were calculated for (a) intra-abdominal extrahepatic recurrences, (b) extra-abdominal and/or hepatic recurrences and (c) all recurrences, and tumour marker levels were analysed.

The sensitivity, specificity and overall accuracy of PET in detecting intra-abdominal extrahepatic CRCR were 82%, 88% and 86%, respectively, compared with 88%, 94% and 92%, respectively, for PET/CT. The corresponding figures for detection of extra-abdominal and/or hepatic CRCR were 74%, 88% and 85% for PET and 95%, 100% and 99% for PET/CT. Considering the entire population, the sensitivity, specificity and overall accuracy of PET were 80%, 69% and 75%, respectively, compared with 89%, 92% and 90%, respectively, for PET/CT. FDG-PET/CT examination correctly detected 40 out of a total of 45 patients with CRCR. Two of five patients with falsely negative FDG-PET/CT findings had local microscopic recurrences and one had miliary liver metastases. Of 39 patients without CRCR, three showed false positive FDG-PET/CT results. Two of these cases were due to increased accumulation in inflammatory foci in the bowel wall, while one was due to haemorrhaging into the adrenal gland.

FDG-PET/CT appears to be a very promising method for distinguishing a viable tumour from fibrous changes, thereby avoiding unnecessary laparotomy.