Can peanut agglutinin distinguish between pseudo and true invasion in colonic adenomas?

We verified the binding of peanut agglutinin (PNA) in 28 pedunculated adenomas (10 with pseudo and 18 with true invasion, respectively) of the large bowel. The distribution of glycoproteins was assessed in the normal mucosa of the stalk, in the surface dysplastic mucosa and in the mucosa of the pseudo-invasion or cancerization areas. The aims of the study were to verify: the PNA role in the differential diagnosis between pseudo and true invasion; the changes in PNA binding during transformation of mucosa from the normal to dysplastic and neoplastic status; the PNA ability as a predictive marker in the neoplastic transformation. The total percentage of PNA positivity in our samples was not significatively higher in carcinomatous than in pseudoinvasive areas (83.3% vs 50%). But the analysis of semiquantitative expression of PNA binding showed that an analogous, or reduced expression of marker in the epithelium in the submucosa compared to the dysplastic surface was consistent with the diagnosis of pseudoinvasion, while its increase strengthened the diagnosis of true invasion. In addition, we found a progressive increase of expression of PNA from the normal to dysplastic and neoplastic mucosa; therefore our data confirmed the quantitative relationship of this marker with malignant transformation. Finally, when we compared the expression of the PNA binding in solely superficial adenomatous tissue of benign and malignant polyps, we found an equal percentage of positive cases (66.6% in the carcinomatous vs 70% in the benign adenomas). Therefore, PNA does not recognize the risk of actual malignant evolution in an adenoma but is indicative of carcinomatous transformation when it is strongly positive.