Ability of CEA blood levels to reflect tumour burden: a study in a human xenograft model.

The relationship of serum carcinoembryonic antigen (CEA) levels to tumour size and antigen content was studied in artificially immune-deprived mice bearing human colonic, breast and lung tumour xenografts. Size was measured as in vivo volume and tumour weight at post-mortem. A multiple implant technique combined with early harvest was used to minimize centrilobular tumour necrosis. CEA was extracted from resected tumours with perchloric acid. A radioimmunoassay using chemical precipitation was used to estimate CEA in blood samples. A correlation was found between CEA blood levels and tumour size in half the tumour lines, in contrast to a recent report (Lewis & Keep, 1981). The CEA content was found to be constant for one tumour line but not another. The possibility that central necrosis in xenograft tumours may account for the discrepancies is discussed. There may be serious limitations for the use of xenograft tumour models for studying the biology of CEA.