Usefulness of galectin-3 immunohistochemistry in differential diagnosis between thyroid follicular carcinoma and follicular adenoma.

Galectin-3 was primarily reported to be a marker distinguishing thyroid adenomas and carcinomas. To check the usefulness of anti-galectin-3 immunohistochemistry, we studied its expression in 42 follicular adenomas and 42 follicular carcinomas. Eight cases out of 42 follicular adenomas (19%) presented focal or diffuse galectin-3 immunoexpression. From 42 cases of follicular carcinomas, six cases did not present galectin-3 immunopositivity at all. Three of these cases were widely invasive (one with focal anaplastic feature and one oxyphilic), and three other ones were minimally invasive. Two other carcinoma cases had only small foci positive with galectin-3 antibody, thirteen cases presented positivity mostly restricted to peripheral part of the tumor and 21 cases possessed diffuse, strong reaction. Two adenomas presented galectin-3 positive foci, and these cells had light nuclear changes superficially suggesting follicular variant of papillary carcinoma, mostly because of nuclear clearing. In these tumors, adenoma diagnosis was supported by experts, but we can not exclude that they represent early phase of malignisation, although such theory needs to be prooved. Our study does not allow to use galectin-3 as a highly specific marker, differentiating between follicular benign and malignant tumor, although it may be used as an additive tool.