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Thorsteinsson, L., O'Dowd, G. M., Harrington, I? M. & Johnson, I? M. The complement regulatory proteins CD46 and CD59, but not CD55, are highly expressed by glandular epithelium of human breast and colorectal tumour tissues. APMIS 106: 869-878, 1998.Three of the proteins protecting cells from autologous lysis by complement are: membrane cofactor protein (MCP; CD46), an inhibitor of the membrane attack complex formation (CD59), and decay accelerating factor (DAF; CD55). We have investigated the expression of these proteins in breast and colorectal carcinoma by immunohistochemistry and immunoblotting of breast tissue for CD46. CD46 was consistently and strongly expressed in the epithelial compartment in 26/28 ductal carcinomas of the breast, 9/9 fibroadenomas, and 911 1 cases of control non-neoplastic breast tissue. CD59 showed a similar degree of expression in the fibroadenomas (9/9), but was less strongly expressed in carcinomatous (22/28) and control (5/11) tissues. In marked contrast, no CD55 expression was detected in tissue from 15 ductal carcinomas. Immunoblotting of breast tissue for CD46 showed the same size of the molecule as for lymphocytes. It had however considerably stronger expression in tumour tissue than in non-neoplastic tissue. CD46 and CD59 were either lacking or only weakly expressed in the epithelial component of control colorectal mucosa: 2/15 and 5/15, respectively. In contrast, tissue samples from colorectal adenocarcinomas showed clear staining for both CD59 (10/18) and, more markedly, CD46 (15/18). There was no association between the pattern or intensity of CD46 and CD59 expression and tumour differentiation. As the complement regulatory proteins CD46 and CD59 are also strongly expressed by trophoblast at the feto-maternal tissue interface, these results support the concept that similar mechanisms are employed both by the genetically dissimilar fetus and certain tumours to evade immune attack by their host.Key words: Breast and colorectal tumours; regulators of complement activation (RCA); membrane cofactor protein (MCP, CD46); decay accelerating factor (DAF, CD55); inhibitor of membrane attack complex formation (CD59).

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A recessive gene on chromosome 17 encodes a protein, known as p53, which normally acts to regulate the cell cycle, its mutation and overexpression being amongst the commonest genetic abnormalities in human malignant neoplasms. As detected by immunolabelling using the anti-p53 protein antibody D07, overexpression was absent from a series of 22 intestinal carcinoid tumours (ten ileal, nine appendiceal, and three colorectal), nine overtly malignant, but was readily demonstrable in five of five colorectal adenocarcinomas, five of six cloacogenic carcinomas, and four of five squamous carcinomas of the anal canal used as controls. These observations are in keeping with previous similar studies of pulmonary carcinoid tumours and suggest possible differences in the pathogenesis of such neoplasms in comparison with non-endocrine differentiated tumours arising at equivalent sites.

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