Sialic acid variants in benign versus malignant colorectal lesions

ABSTRACT

The histochemical mucin structure of colorectal lesions has been subject to several studies. Some reports relate changes in mucin pattern to the grade of epithelial dysplasia. Alterations in sialomucin with both its O-and N-residues have been described in colonic malignancy. This work was, thus, carried out on 50 benign and malignant colorectal lesions to study the histochemical structure of sialic acid, by applying the PAT/KPH/PAS technique [introducing a counterstain to the original method described] and the mPAS technique for demonstrating the O-and N-acetyl residues respectively. The PAT/KOH/PAS technique was more informative. It gave a spectrum of colours ranging from red through purple to blue, reflecting normal, partial loss and absence of the O-acetyl residue respectively. In contrast, however, were the results of the mPAS technique. Positive cases have shown only scattered foci of mild positivity in the form of pale, red granular deposits. Among all non-neoplastic lesions examined [n = 9], the PAT/KOH/PAS technique gave a red reaction reflecting normal pattern. In adenomatous polyps without atypia [n = 10] 70% gave a normal, red, reaction while in 30% the reaction was purple. Polyps with atypia [n = 12] revealed more loss of O-residue in cases showing atypia. There was also a notable loss of O-residue with higher grades of malignancy. None of the malignant cases examined revealed a normal red reaction [n = 19], while 25% of well, 75% of moderately and 100% of poorly differentiated adenocarcinomas gave a blue mucin reaction. Results confirm higher loss of O-acetyl residue with severe dysplasia and less differentiated malignant tumors of the colon. The PAT/KOH/PAS technique can, thus, be helpful in predicting the outcome of colonic adenoma by assuming that a red colour reaction reflects its benign nature, while a purple to blue reaction implies the danger of malignant transformation. It can also be used in the interpretation of equivocal malignancies in small colonoscopic biopsies