Comparison of different techniques for detection of Gal-GalNAc, an early marker of colonic neoplasia

The tumor marker, D-galactose-beta[1-3]-N-acetyl-D-galactosamine (Gal-GalNA c, also known as T-antigen) can be identified by a very simple galactose ox idase-Schiff's (GOS) reaction either on tissues or on rectal mucus samples from patients with colorectal neoplasms. Gal-GalNAc is expressed in the neo plastic mucosa as well as the remote non-neoplastic mucosa. It is, however, not expressed in colonic mucosa of normal subjects. We studied the express ion of Gal-GalNAc by GOS reaction, lectin reactivity and immunocytochemistr y in 10 normal, 45 precancerous [5 Crohn's disease, 15 ulcerative colitis ( 5 without dysplasia and 10 with dysplasia), 25 tubular adenomas], and 25 ad enocarcinoma cases. Normal mucosa remote from tubular adenoma and adenocarc inoma was also studied. The GOS method was compared with reactivity of the lectin jacalin and immunostaining with antibody to T antigen (Anti-Tag Ab). GOS reaction was negative in all of the 10 normal specimens. Of the 5 Croh n's disease specimens, 2 were positive and 3 negative. In the 5 ulcerative colitis cases without dysplasia, positive reaction was seen in 2 cases and negative in 3. Of the 10 cases of ulcerative colitis with dysplasia, 5 show ed positivity in dysplastic areas, and 3 of these were also positive in rem ote non dysplastic mucosa. Twenty of 25 tubular adenomas yielded a positive reaction in the adenoma, 14 of them showing positivity also in remote muco sa; 3 cases showed a positive reaction only in remote mucosa. Of the 25 ade nocarcinomas, 21 showed a positive reaction in the adenocarcinoma as well a s the remote mucosa. GOS reaction was intense in well differentiated adenoc arcinoma and weak in poorly differentiated adenocarcinoma. Intense reaction was also seen in the intracellular mucus of some aberrant crypts and morph ologically normal crypts remote from adenocarcinoma and tubular adenoma. GO S reaction showed an overall sensitivity of 75.7% and specificity of 100% f or cancer and precancerous lesions. Jacalin reactivity was slightly more se nsitive (84.3%) but less specific (80%) and Tag Ab reactivity even less sen sitive (50%) but as specific (100%) for neoplastic and dysplastic mucosa. W e conclude that the detection of the carbohydrate moiety Gal-GalNAc varies with the technique used. Compared to other techniques, GOS reaction is extr emely simple and has a high degree of sensitivity and specificity. It can b e used for detection of this tumor marker in remote non-neoplastic mucosa o f patients with neoplasia or at risk of developing neoplasia. It, therefore , could be used as a cost effective screening test in rectal biopsy specime ns of such patients.