Eight metaplastic polyps, 16 tubulo-villous adenomas and 20 adenocarcinomas, all from the colon, were examined for the presence of a number of tumour associated antigens. Specific antibodies, raised in rabbits, were used to detect the antigens in formalin fixed (pH 7.0) paraffin embedded material. Antisera were directed against carcino-embryonic antigen (CEA), colon specific antigen (M. Wt) (CSA), α-fetoprotein, pregnancy specific β-lipoprotein 1 (SP 1), human β-chorionic gonadotrophin (HCG), human placental lactogen (HPL), and placental alkaline phosphatase (P Alk P). Antisera against isoferritins, reported in some non-gastrointestinal tumours and transferrin, normally found in small intestinal epithelium were also used. Specificity of antibodies was checked in other systems (RIA and immunodiffusion plates) and using appropriate fixed substrate tissues in the P.A.P. technique. Detection and localization of antigens in tissues was made using the P.A.P. (peroxidase-antiperoxidase) enzyme bridge immunohistochemical method. Results are shown in Tables 1 and 2. Placental alkaline phosphatase was found in only 2 specimens and is not included in the tables. Table 1 Antigen No. cases Condition 0 1 2 3 4 5 6 7 16 TVA 1 3 1 3 1 1 1 6 20 Cancers 0 2 2 0 1 3 3 9 8 Metaplastic polyps 0 1 5 0 0 0 0 2 Table 2 Antigen No. cases Condition SPI HPL βHGG CEA CSA AFP Transfer Ferrit 16 TVA 6 11 10 16 14 9 9 9 20 Cancers 12 9 10 20 20 12 13 10 8 Metaplastic polyps 2 7 2 8 7 2 2 2 There appears to be no difference in either number of antigens present, or in the number of cases positive for each antigen, between cancers and tubulo-villous adenomas, but the majority of metaplastic polyps show only CEA and HPL positivity. The 2 metaplastic polyps showing a full range of positivity were atypical in that they were greater than 5 mm in diameter and had some features of adenomatous polyps, although they appeared as typical metaplastic polyps to an experienced gastrointestinal surgeon. The findings have shown a remarkable similarity between polyps and cancer which strengthens the concept of the relationship between adenomatous polyps and carcinoma of the colon, but have revealed no definite antigenic marker of malignant transformation. It would appear that the difference in behaviour is not related to antigenic profile. Despite the literature stressing the benign nature of metaplastic polyps, a more cautious appraisal of those above 5 mm diameter may be indicated.
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