FDGPET in the Diagnosis and Staging of Recurrent Colorectal Cancer

Early detection of recurrent disease is of primary importance because it may lead to a cure in up to 25% of patients. Surgical or medical treatment with the intent to improve survival and the quality of life should be guided by the accurate staging of disease. The size and number of hepatic metastases and the presence of extrahepatic disease affect the prognosis. The prognosis is poor if extrahepatic metastases are present, and this is believed to be a contraindication to hepatic resection.255

Iterative measurement of CEA is a useful, albeit imperfect, method to monitor the detection of recurrence, with a sensitivity of 59% and specificity of 84%.256 Barium studies have been reported to be only 49% sensitive, 85% specific, and 80% accurate for overall recurrence.257 A strategy in which increased CEA levels trigger the ordering of a PET study is limited by the diagnostic performance of CEA itself, which is far from optimal.

CT has an accuracy of 25% to 73% for localizing recurrence, but it fails to demonstrate hepatic metastases in up to 7% of patients and underestimates the number of lobes involved in up to 33% of patients. Metastases to the peritoneum, mesentery, and lymph nodes are commonly missed on CT, as well as the differentiation of postsurgical changes from local tumor recurrence.258,259 CT portography (superior mesenteric arterial portography) is more sensitive (80% to 90%) than CT (70% to 80%) for detection of hepatic metas-

tases, but there are many false-positive findings, which lower the positive predictive value.260,261 There are also limitations in accurate operative staging because of adhesions or the site of the surgical incision (transverse upper abdominal for liver resection). Shiepers et al.262 studied 76 patients and found that the accuracy of FDG-PET and CT were 95% and 65%, respectively, for differentiation of scar from local recurrence.

Huebner et al.,263 in a meta-analysis review of 11 articles, reported that the sensitivity and specificity for detecting recurrent colorectal cancer with FDG-PET were 97% and 76%, respectively, and for liver and local pelvic recurrences FDG-PET had specificities of 99% and 98%. Whiteford et al.264 demonstrated that the sensitivity of FDG-PET imaging for detection of mucinous adenocarcinoma was significantly lower than for nonmucinous adenocarcinoma, 58% and 92%, respectively, mainly because of the relative hypocellularity of these tumors.265

The high diagnostic accuracy of FDG-PET for detecting liver metastases was confirmed by Kinkel et al.,266 who compared noninvasive imaging modalities (US, CT, MRI, and FDG-PET) for the detection of hepatic metastases from colorectal, gastric, and esophageal cancers. They found that FDG-PET had the highest sensitivity (90%), compared with 76% for MRI, 72% for CT, and 55% for US. Delbeke et al.267 reported that FDG-PET had a higher accuracy (92%) than CT (78%) and CT portography (80%) for detection of hepatic metastases. Although the sensitivity of FDG-PET (91%) was lower than that of CT portography (97%), the specificity was much higher, particularly at postsurgical sites.

Ogunbiyi et al.268 compared the sensitivity of FDG-PET and CT in local recurrence (91% versus 52%) and in hepatic lesions (95% versus 74%). Rydzewski et al.269 found that the PPV of FDG-PET for characterizing liver lesions was similar to that of intraoperative ultrasonography (US) (93% and 89%, respectively) and superior to CT and MRI imaging (Table 33.12).

A major advantage of FDG-PET is its ability to detect extrahepatic disease not discovered by the other modalities. Valk et al.270 compared the sensitivity of FDG-PET and CT for specific anatomic locations and found that FDG-PET was more sensitive than CT in all locations except the lung, where the two modalities were equivalent. The largest difference between PET and CT was found in the abdomen, pelvis, and retroperitoneum, where more than one-third of PET-positive lesions were negative by CT. PET was also more specific than CT at all sites except the retroperitoneum.

Delbeke et al.267 concluded that, outside of the liver, FDG-PET was especially helpful in detecting nodal involvement, differentiating local recurrence from postsurgical changes, evaluating the malignancy of indeterminate pulmonary nodules, and detecting distant metastases in the chest, abdomen, or pelvis.

Gambhir et al.,271 in a review of 2,244 patient studies, reported that the sensitivity and specificity for FDG-PET were 94% and 87%, respectively, compared with 79% and 73% for CT. Flanagan et al.272 reported the use of FDG-PET in 22 patients with unexplained elevation of CEA serum levels after resection of colorectal carcinoma with no abnormal findings on conventional workup, including CT. The sensitivity of FDG-PET in these patients was 100%, the specificity 71%, and the PPV 89%. Valk et al.270 reported a sensitivity of 93% and a specificity of 92% in a similar group of 18 patients.

Flamen et al.273 used FDG-PET to study 50 patients with elevated CEA and negative (n = 31) or equivocal (n = 19) findings on conventional imaging and found a sensitivity of 79% for the patients and 75% for the lesions. Cohade et al.,274 in a study of 45 patients, showed that PET/CT integrated imaging reduced the frequency of equivocal and probable lesion characterization by 50% compared with PET alone. This hybrid modality increased the number of definite locations by 25% and increased the overall correct staging from 78% to 89%.

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