We have used an indirect immunofluorescence assay to demonstrate the cell membrane expression of carcinoembryonic antigen (CEA) by a pre-malignant colorectal adenoma derived epithelial cell line (PC/AA) and three colorectal carcinoma cell lines (HT29, PC/JW and PC/JW/FI). The results obtained indicated that CEA may be used as a marker for tumour progression up to the point of malignant transformation, after which the selection for anaplastic variants during continuous in vitro culture may result in the subsequent reduction of cell membrane CEA expression. The percentage of PC/AA cells expressing cell membrane CEA increased from 23.1% of diploid early passage (passage 18) cells to 56.0% of aneuploid late passage (passage 58) cells. Although non-tumorigenic, the proportion of PC/AA cells expressing cell membrane CEA at late passage corresponded to that for the PC/JW carcinoma line (56.2%) and is further evidence for the progression of PC/AA in culture. A 3T3 feeder-independent variant of PC/JW (PC/JW/FI) demonstrated a similar percentage of CEA-positive cells as the parental line for the first 21 passages without feeder support, but by passage 27 without 3T3 feeders only 35.3% of cells stained positive. This could be restored to 62.0% by continuous treatment with sodium butyrate (2 mM). A differential growth response to sodium butyrate was noted for the pre-malignant adenoma cell line PC/AA and the carcinoma lines HT29 and PC/JW/FI. Concentrations of sodium butyrate (2 mM) that killed early passage PC/AA cells allowed the late passage PC/AA cells and the carcinoma lines to proliferate, raising the possibility of sodium butyrate acting as a tumour promotor in the human colorectum.

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