Follicular Thyroid Adenoma and Follicular Thyroid Carcinoma—A Common or Distinct Background? Loss of Heterozygosity in Comprehensive Microarray Study

SIMPLE SUMMARY: Approximately 50% of 60-year-old persons have thyroid nodules that in 7–15% may be thyroid cancer. Diagnosis of follicular thyroid adenoma (FTA) and follicular thyroid cancer (FTC) is particularly challenging. Furthermore, it is not clear whether they share a common or distinct background. The study aimed to compare FTA and FTC using the comprehensive microarray for the first time and to identify recurrent regions of loss of heterozygosity. We found that FTA and FTC may share a common genetic background—including the same LOH in 16p12.1, which encompasses many cancer-related genes. However, differentiating rearrangements may also be detected, such as LOH in 11p11.2-p11.12 only in FTA patients (56% vs. 0%) and LOH in 12q24.11-q24.13 detected more often in FTC (37.5% vs. 6.3% in FTA). Genomic screening may show the complexity of genetic background in follicular thyroid lesions and enable the identification of new genetic rearrangements participating in FTC pathogenesis. ABSTRACT: Pre- and postsurgical differentiation between follicular thyroid adenoma (FTA) and follicular thyroid cancer (FTC) represents a significant diagnostic challenge. Furthermore, it remains unclear whether they share a common or distinct background and what the mechanisms underlying follicular thyroid lesions malignancy are. The study aimed to compare FTA and FTC by the comprehensive microarray and to identify recurrent regions of loss of heterozygosity (LOH). We analyzed formalin-fixed paraffin-embedded (FFPE) samples acquired from 32 Caucasian patients diagnosed with FTA (16) and FTC (16). We used the OncoScan™ microarray assay (Affymetrix, USA), using highly multiplexed molecular inversion probes for single nucleotide polymorphism (SNP). The total number of LOH was higher in FTC compared with FTA (18 vs. 15). The most common LOH present in 21 cases, in both FTA (10 cases) and FTC (11 cases), was 16p12.1, which encompasses many cancer-related genes, such as TP53, and was followed by 3p21.31. The only LOH present exclusively in FTA patients (56% vs. 0%) was 11p11.2-p11.12. The alteration which tended to be detected more often in FTC (6 vs. 1 in FTA) was 12q24.11-q24.13 overlapping FOXN4, MYL2, PTPN11 genes. FTA and FTC may share a common genetic background, even though differentiating rearrangements may also be detected.