Semiquantitative SPECT tumor uptake of technetium-99m-labeled anti-CEA monoclonal antibody in colorectal tumor.

UNLABELLED

Technetium-99m-BW431/26 images were compared to images of resected tumor specimens to evaluate the efficacy and accuracy of SPECT imaging of colorectal carcinoma.

METHODS

Immunoscintigraphy with 99mTc-BW431/26 was performed on seven patients with colorectal carcinoma and one patient with a benign colorectal tumor. Accumulation of 99mTc-BW431/26 in the tumor was expressed as the tumor-to-normal tissue count ratio (SPECT T/N ratio) calculated by a region of interest method on the SPECT images obtained 24 hr after administration of 99mTc-BW431/26. All patients underwent research of the tumor immediately after 24-hr imaging, and the radioactivity in tumor specimen and normal tissue was measured to calculate the tissue T/N ratio.

RESULTS

SPECT demonstrated definite increased tracer uptake by the tumor in all colorectal cancer patients. The benign lesion showed tracer uptake to a lesser extent. SPECT, however, failed to visualize a 10-mm lesion in a patient with familial adenomatous polyposis despite a tissue T/N ratio of 4.8, while autoradiography showed radioactivity uptake in the polyps.

CONCLUSION

Although SPECT has limitations in detecting small lesions because of its limited spatial resolution, T/N ratios could be measured exactly by SPECT if the lesion is of a certain volume. SPECT imaging with 99mTc-BW431/26 can precisely evaluate tracer uptake in tumors and predict the efficacy of radioimmunotherapy in patients with colorectal cancer.