SPECT with I-123 labeled F(ab')/sub 2/ fragments from monoclonal anti-CEA antibodies in colon carcinoma

Eleven patients with colorectal carcinoma were studied, 4 with primary, 7 with recurrent (1) or metastatic lesions. After injection of 1,5mg of F(ab')/sub 2/ of monoclonal anti-CEA antibodied No 35 (n=9) or 202 (n=2) labeled with I-123 (p,5n) (3-4mCi) whole body distribution was measured on anterior and posterior views at 1,6,24,48 h. SPECT was performed with a dual head device at 6,24,48 h. F(ab')/sub 2/ No 202 showed relatively high bone marrow uptake and high urinary activity (74% of injected activity in 3 days), but low liver activity (x-bar 14% of whole body activity at 24 h ). With F(ab')/sub 2/ No 35 bone marrow activity was lower, mean relative liver uptake 17% and mean urinary activity 24%. In 2 surgical specimens tumor to normal tissue ratios were measured at day 5 post injection and found to be 6,8,15,9 for one, 3,5,7,2 for the other in comparison with mucosa, serosa, fat and blood respectively. All 5 localized carcinoma were detected by ECT, the best images being obtained at 24 h. On the 6 h scans 4 patients with liver metastases showed cold lesions which became positive on the 24 h ECT in 2 of them whereas the 2 others remained doubtful. 2 patients with liver involvement showed no uptake. In 1 patient under therapy 2 small lung metastases were not detected. 2/2 bone metastases showed tracer uptake 1 of them was previously unknown. High quality images can be obtained with this method already at 24 h but the detection of metastases especially in the liver is sometimes difficult