Galectin-3 and HBME-1 expression in well-differentiated thyroid tumors with follicular architecture of uncertain malignant potential

Well-differentiated encapsulated tumors of the thyroid gland with a follicular architecture may cause diagnostic difficulties due to the presence of incomplete or equivocal capsular penetration—which may induce the suspicion of follicular carcinoma—or the occurrence of focal nuclear changes such as clearing, overlapping, grooves and pseudoinclusions, which may raise the possibility of the follicular variant of papillary carcinoma. Depending on the severity of these changes and the bias of the observer, terms such as atypical adenoma, 'hybrid' carcinoma, and—more recently—well-differentiated carcinoma not otherwise specified were proposed. In a recent editorial from the Chernobyl Pathologists Group the suggestion was made to label tumors with 'borderline' features as well-differentiated tumor of uncertain malignant potential (WDT-UMP) in the presence of questionable papillary carcinoma-type nuclear changes with or without questionable capsular penetration, or follicular tumor of uncertain malignant potential (FT-UMP) in the presence of questionable capsular penetration without nuclear changes.

Several immunocytochemical markers of malignancy have been claimed to be useful to distinguish follicular adenoma from carcinoma and also to identify papillary carcinoma and its variants, both in surgical and cytological specimens. These include Galectin-3,HBME-1,cytokeratin 19, thyroperoxidase, and high mobility group (HMG)-Y proteins.

Galectin-3 is a member of a family of -galactoside binding animal lectins. This protein is expressed in many tissues and cells at both nuclear and cytoplasmic levels and has multiple functions, including cell–cell and cell–matrix adhesion, cell growth, neoplastic transformation and spread, cell cycle regulation and apoptosis, and cell repair processes. Galectin-3 has been found to be increased in several human malignant tumors, including well-differentiated follicular-derived thyroid carcinomas. HBME-1 was originally described as a marker of normal and malignant mesothelial cells, since it recognizes a currently unknown antigen expressed by those cells. It was later shown to also stain most papillary thyroid carcinomas, and also a fraction of follicular carcinomas, while adenomas are generally negative. In a recent study on oxyphilic tumors of the thyroid,Galectin-3 and HBME-1 expression were found to be related to molecular alterations such as PAX8-PPARgamma translocations and ras oncogene mutations.

The aim of the present study was to investigate the expression and the possible diagnostic role of these two markers in a series of well-differentiated thyroid neoplasms with a follicular architecture that fulfilled the criteria for WDT-UMP or FT-UMP, as proposed by Williams et al.

Tissues

The diagnosis was based on the proposed criteria for these tumors. In particular, WDT-UMP was represented by an encapsulated tumor composed of follicular cells having incompletely developed papillary carcinoma-type nuclear changes. In these tumors, no blood vessel invasion was present, while capsular penetration was either absent or questionable. FT-UMP was defined as an encapsulated tumor with follicular architecture, composed of conventional or oxyphilic cells, and having incomplete or questionable capsular penetration, but neither vascular invasion nor papillary carcinoma-type nuclear changes. Based on these criteria, 13 cases qualified as WDT-UMP (one of these was a small nodule in the context of Hashimoto's thyroiditis) and eight as FT-UMP. In all, 14 cases of follicular variant of papillary carcinoma and 15 follicular adenomas were collected from the same Institutions and served as control groups. All cases had hematoxylin & eosin (H&E) stains available for review and paraffin blocks for immunohistochemical stainings.

Immunohistochemistry

A purified monoclonal antibody to Galectin-3 was used at the dilution of 1/200, as previously described. This monoclonal is now commercially available (Mabtech, Naka, Sweden). HBME-1 antibody was purchased from DakoCytomation (Glostrup, Denmark) and used at the dilution of 1/50. Both markers were revealed with a biotin-free immunoperoxidase procedure (EnVision, DakoCytomation), preceded by heat-induced antigen retrieval (three 3-min microwave oven passages at 750 W in citrate buffer). Positive controls for immunohistochemistry were a papillary thyroid carcinoma for Galectin-3 and a pleural mesothelioma for HBME-1. Macrophages at the periphery of goiter nodules and endothelial cells served as positive internal controls in most cases. The immunoreactivity was scored as negative, focally positive (+: less than 25%), positive (++: 25–50%) or diffusely positive (+++: more than 75%), based on the extent of the reaction. A case was scored as positive only when strong signals in the cytoplasm or along the cell membrane were detected for Galectin-3 and HBME-1, respectively.

Source :

Modern Pathology (2005) 18, advance online publication.