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EARLY EXPRESSION OF bcl‐2 PROTEIN IN THE ADENOMA–CARCINOMA SEQUENCE OF COLORECTAL NEOPLASIA

bcl‐2 was originally identified as an oncogene involved in follicular lymphomas as a result of chromosomal translocation (14;18). It is now believed that bcl‐2 is implicated in the regulation of cell death by inhibiting apoptosis and that its expression is not restricted to haematopoietic cells, but is also present in many epithelia and mesenchymal tissues. Recent studies have analysed the expression of this molecule in a variety of non‐lymphoid malignancies including lung, breast, prostate, and nasopharyngeal carcinomas and neuroblastoma. In the present study, 50 colorectal adenomas, 10 hyperplastic polyps, and 142 carcinomas, including 25 arising from pre‐existing adenomas, were examined using an antibody detecting the bcl‐2 protein product. In non‐neoplastic mucosa, bcl‐2 was expressed in the crypt cells only, whilst the more differentiated surface epithelial cells lacked any demonstrable bcl‐2. Forty‐one of the 50 adenomas (82 per cent) and 48 of the 142 carcinomas were positive for bcl‐2 expression. All hyperplastic polyps were negative. A reciprocal relationship was found between bcl‐2 reactivity and p53 overexpression, as detected by DO7 antibody, in approximately 65 per cent of the cases. The bcl‐2‐positive/p53‐negative subgroup showed a strong correlation (P=0·0056) with negative lymph node status (Dukes' A and B), implying a less aggressive pathway of neoplastic transformation.