Tumor scintigraphy with 131I anti CEA monoclonal antibodies and F(ab')2 in colorectal cancer.

In 14 patients with proven local recurrence of colorectal cancer or metastases in liver and/or lungs, the sensitivity (SE) in detecting tumor sites was estimated in a single-blind study using conventional planar whole body scintigraphy. Nine patients received F(ab')2 and five received MAB by intravenous infusion over 30 min with a dose of 40-200 MBq after skin testing and thyroid blocking, scanning was performed 1-7 days later. All but one patient had elevated plasma CEA levels with a mean of 25.5 +/- 31.9 ng/ml. The scans were interpreted by two independent observers. In five of the nine patients receiving F(ab')2, the tumor site could be visualized, yielding a sensitivity of 55%. No tumor sites were identified with MAB. The highest tumor uptake was recorded in a patient with additional ovarian cancer with the activity accumulating in the ovarian cancer. The optimum time for imaging was 3 or 4 days after injection. There was no correlation between positive imaging and plasma CEA levels which ranged from 1.9 ng/ml to 100 ng/ml in the positive cases. The thyroid uptake on the sixth day was 0.68% +/- 0.2% of the total dose given despite thyroid blocking. Bone uptake of 131I was also observed, this was mild in four patients, moderate in three but high in one patient, especially on days one to four. Thus, only anti-CEA F(ab')2 seem to be of clinical interest for further evaluation in localizing colorectal cancer. Regarding the still low sensitivity of 55%, further improvement can be expected by gaining experience, using more appropriate isotopes such as 111In and SPECT. The estimated radiation side effects on thyroid and bone marrow are only modest.