Is there a role for (99m)Tc-anti-CEA monoclonal antibody imaging in the diagnosis of recurrent colorectal carcinoma?

Aim: To evaluate the usefulness of immunoscintigraphy with an anti-CEA monoclonal antibody fragment labelled with (99m)Tc for early detection of colorectal recurrence in patients with rising serum CEA levels.

Methods: Fifty-one consecutive patients (27 women, 24 men) with colorectal cancer (mean age 68.9+/-10.2 years) and rising CEA levels (16.2+/-18.2 ng/ml) were prospectively studied. Two immunoscintigraphy studies were performed in 8 patients (n=59). Immunoscintigraphy was performed after i.v. injection of 925 MBq of anti-CEA monoclonal antibody. Planar images of the thorax, abdomen and pelvis, as well as SPECT of the abdomen and pelvis were obtained at 4 and 24 hours after injection. In all cases an abdominal CT scan was previously performed. Findings were validated by histopathological analysis (28 cases) or by imaging and clinical follow-up of at least 6 months following the immunoscintigraphy (31 cases).

Results: Forty-one patients did not show recurrence during follow-up. We found 18 cases with confirmed diagnosis of extrahepatic abdominal or pelvic diseases, 11 cases with liver metastases, 9 in the thorax and 2 in the bone. In patients with pelvic and extrahepatic abdominal disease, immunoscintigraphy was positive in 18 cases (14 true positive, 4 false positive). From the 14 true positive only 7 cases had been detected by CT. Immunoscintigraphy was negative in the remaining 41 cases (37 true negative, 4 false negative). Therefore, the sensitivity and specificity for immunoscintigraphy in extrahepatic abdominal and pelvic disease were 78% and 90%, respectively. CT results showed a lower sensitivity of 61% (p<0.05) and specificity of 83%. Liver metastases were detected by CT in 9 cases, but only 2 of these were identified using immunoscintigraphy.

Conclusion: Scintigraphy with anti-CEA monoclonal antibody fragment labelled with (99m)Tc is superior to CT for the detection of pelvic and extrahepatic abdominal recurrence of colorectal cancer, while CT is more sensitive in the detection of liver and lung metastases. Immunoscintigraphy has a limited usefulness in the detection of distant metastases, but it may be helpful in the diagnosis of suspected colorectal recurrence in patients with non-conclusive CT findings, when FDG-PET is not available.