Heterogeneous expression of two oncodevelopmental antigens, CEA and SSEA-1, in colorectal cancer

Colorectal carcinomas are composed of heterogeneous cell subpopulations which may be instrumental in conferring metastatic potential and therapeutic refractoriness to these tumours. To assess cellular heterogeneity, the expression has been examined of two oncodevelopmental antigens, carcinoembryonic antigen (CEA) and stage-specific embryonic antigen 1 (SSEA-1), by double immunofluorescence microscopy on 11 human colorectal carcinomas. Although both antigens were expressed in each tumour, their regional and cellular locations differed considerably. SSEA-1 expression was rarely expressed in poorly differentiated cancers but was enhanced with increasing degrees of differentiation. CEA expression was independent of histological differentiation. SSEA-1 was expressed with similar frequency in cell membranes, cytoplasm, and glandular contents regardless of degree of differentiation. Cytoplasmic staining with CEA however, was limited to more poorly differentiated tumours. In normal mucosa remote from the tumours and transitional mucosa adjacent to them, SSEA-1 stained only a few lower crypts whereas CEA stained a majority of both upper and lower crypts. Although biochemical studies have indicated that the SSEA-1 epitope may reside on CEA molecules, the fact that colon cancer tissues express these two antigens quite heterogeneously suggests differences in antigenic processing which may be dependent upon the degree of cellular differentiation.