A prospective study of the use of 111In-labelled monoclonal antibody against carcino-embryonic antigen in colorectal cancer and of some biological factors affecting its uptake.

This prospective study of radioimmunoscintigraphy using 111In-labelled, C46, a monoclonal antibody against carcino embryonic antigen, CEA, was undertaken in 23 patients with colorectal cancer, 18 with primary carcinomas, 3 with recurrences and 2 with metastases. A sensitivity of 95% and an accuracy of 91% was found. New observations through the use of two administered doses of antibody and the analysis of surgical specimens showed that for the low dose of antibody (average 0.76 mg) tumour uptake was 1.14 x 10(-2)% of the injected dose per gram, whereas on the higher dose (average 4.67 mg) the average tumour uptake was 6.77% (same units) p less than 0.01. Thus a six-fold increase of antibody caused a six-fold increase in tumour uptake, but no change was seen in the tumour to mucosa ratio 4.8 +/- 0.5 (low dose) and 4.0 +/- 1.0 (high dose). A further observation was that well and moderately differentiated tumours took up about four times more than poorly differentiated tumours (p less than 0.05). It was also found that tumour free lymph nodes had a six-fold greater uptake than tumour involved nodes (p less than 0.05) confirming other work with anti-CEA monoclonal antibody. In conclusion, although biological factors influence its efficacy, 111In labelled C46 anti-CEA is a suitable radiopharmaceutical for the radioimmunoscintigraphy of colorectal cancer.