Patterns of FOXE1 expression in papillary thyroid carcinoma by immunohistochemistry

Abstract

Background: FOXE1, a thyroid-specific transcription factor also known as TTF-2, was recently identified as a major genetic risk factor for papillary thyroid carcinoma (PTC). Its role in thyroid carcinogenesis, however, remains unknown. The purpose of the present study was to assess the relationship between the FOXE1 immunohistochemical features and the clinical and genetic characteristics of PTC.

Methods: Immunohistochemical staining of FOXE1 was performed in 48 PTC cases. Two single nucleotide polymorphisms immediately inside (rs1867277) or in the vicinity (rs965513) of the FOXE1 gene were genotyped by direct sequencing. Histopathological, clinical, and genetic data were included in statistical analyses.

Results: FOXE1 exhibited cytoplasmic overexpression in tumor tissue compared to the normal counterpart (p<0.001). Both cancer and normal thyroid cells demonstrated the highest FOXE1 scores in the areas closest to the tumor border (<300 μm) compared with more distant areas (p<0.001). No differences in FOXE1 staining distributions were found between microcarcinomas and PTC of larger size, between different histopathological variants of PTC, and encapsulated and nonencapsulated tumors. Multivariate regression analysis revealed that nuclear FOXE1 expression in neoplastic cells in the vicinity of the tumor border independently associated with the genotype at rs1867277 (the dominant model of inheritance, p=0.037) and tumor multifocality (p=0.032), and with marginal significance with capsular invasion (p=0.051).

Conclusions: FOXE1 overexpression and translocation to the cytoplasm are phenotypic hallmarks of tumor cells suggesting that FOXE1 is involved in the pathogenesis of PTC. Nuclear FOXE1 expression in tumor cells in the vicinity of the PTC border is associated with the presence of a risk allele of rs1867277 (c.-238G>A) in the 5' untranslated region of the FOXE1 gene, as well as with pathological characteristics of PTC, suggesting possible FOXE1 involvement in the facilitation of tumor development beginning at an early stage.

FIG. 1.

Expression patterns of FOXE1 and MCM2 in papillary thyroid carcinoma (PTC) and adjacent nonneoplastic thyroid. (a) Low-power view of encapsulated PTC and surrounding thyroid tissues stained with hematoxylin and eosin. (b) Immunohistochemical FOXE1 staining demonstrates the highest expression at the tumor/normal tissue interface in both counterparts. (c–f) High-power fields of FOXE1 expression in the N distant, N close, T close, and T distant zones, respectively. (g) Panoramic view of MCM2 immunostaining in PTC showing prominent labeling of cancer tissue as compared to the very low index in the normal counterpart. (h–k) High-power fields of MCM2 expression in the N distant, N close, T close, and T distant zones, respectively. Serial sections, scale bars 300 μm (a, b, g) and 30 μm (c–f, h–k).

FIG. 2.

FOXE1 immunoreactivity scores in PTC and adjacent normal thyroid tissue. Box-and-whisker/dot plots showing the distributions of cytoplasmic and nuclear FOXE1 scores in the close and distant zones of normal thyroid (N) and tumor tissue (T). The bottom and top lines of the box represent the values corresponding to the 25th and the 75th percentiles, respectively; position of the notch represents the median; a small inner square indicates the mean; the range represented by the whiskers corresponds to the 10th and the 90th percentiles; the crosses correspond to the 1st and the 99th percentiles. Differences between the scores were evaluated using the Mann-Whitney U-test: *p<0.01; **p<0.05; ns, nonsignificant.