Detection of apoptosis in colorectal carcinoma by light microscopy and in situ end labelling.

An in situ end labelling reaction (ISEL) was recently described for the detection of apoptotic cells in histologic sections. We compared the efficiency and reproducibility of this assay with those of routine light microscopy using hematoxylin and eosin (H&E) in the quantitation of apoptotic cells in colorectal cancer. Paraffin-embedded archival tissues from 15 colorectal carcinomas were used in the study. ISEL was performed using terminal deoxynucleotidyl transferase, biotinylated deoxyuridine triphosphate and streptavidin-alkaline phosphatase. Apoptotic indices determined by the two assays showed a strong positive correlation (Pearson coefficient 0.82), with the ISEL assay detecting twice the number of apoptotic cells as that seen with H&E staining. Both assays showed significant interobserver and intraobserver variation, while the ISEL assay also showed considerable interassay variability and was less cost-effective than H&E in the detection of apoptotic cells. In the light microscopic quantitation of apoptosis in colorectal tumors, the ISEL assay offered no greater reproducibility, and was less cost-effective, than routine H&E staining.