Can malignancy in insulinoma be predicted by the expression patterns of beta 1,6 branching of asparagine-linked oligosaccharides and polysialic acid of the neural cell adhesion molecule?

We analysed the value of the expression of beta 1,6 branching of asparagine-linked oligosaccharide chains and polysialic acid of the neural cell adhesion molecule (NCAM) in predicting malignant behaviour in human insulinomas, as these glycoconjugates have been associated with invasive growth and metastatic potential. Fifty-three insulinomas from patients with well-documented clinical and follow-up data were investigated. Lectin histochemical staining for beta 1,6 branches revealed that 11 (74%) of the 15 malignant insulinomas stained more strongly than normal beta cells. However, in as many as 23 (63.1%) of the 38 benign insulinomas with a disease-free follow up for 4-18 years (average 8 years), a staining intensity equivalent to that of malignant tumours was found. Two (13%) of the malignant insulinomas and 1 of the 4 liver metastases studied were unstained. None of the 53 insulinomas (and the rat RIN insulinoma) re-expressed polysialic acid as demonstrated by immunohistochemistry and Western blotting with the monoclonal antibody 735. Therefore, histochemical staining for beta 1,6 branches and immunohistochemistry for polysialic acid are unlikely to be of value as prognostic indicators for patients with insulinomas.