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

Abstract

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.