Epigenetic Alterations and Canonical Pathway Disruption in Papillary Thyroid Cancer: A Genome-wide Methylation Analysis.

ABSTRACT

BACKGROUND: Alterations in DNA methylation have been demonstrated in a variety of malignancies, including papillary thyroid cancer (PTC). The full extent of dysregulation in PTC and the downstream affected pathways remains unclear. Here we report a genome-wide analysis of PTC methylation, the dysregulation of various canonical pathways, and assess its potential as a diagnostic test. METHODS: A discovery set utilized 49 PTCs and matched normal controls from The Cancer Genome Atlas. Another set of 16 PTCs and 13 normal controls were used as a replication set. Genome-wide methylation analysis was done using Illumina 450 K methylation chips. Differentially methylated loci (DML) were identified by comparing PTC and matched normal tissues. DML were defined as false-discovery rate p < 0.05 and absolute Δß ≥ 0.2. DML were then analyzed for pathway and disease commonalities using Qiagen Ingenuity Pathway Analysis. RESULTS: Of 485,577 CpG sites analyzed, 1226 DML were identified in our discovery and replication sets, and 1061 (86.5 %) DML showed hypomethylation when comparing tumor with normal tissue. Support vector machine classification was able to differentiate benign from malignant tissue in 107 (94.7 %) of 113 tested samples, including 15 (83.3 %) of 18 samples lacking a clearly deleterious mutation. Statistically significant associations with multiple canonical pathways, diseases, and biofunctions were observed including PI3K, PTEN, wnt/ß-catenin, and p53. CONCLUSIONS: Epigenetic dysregulation of multiple canonical pathways are associated with the development of PTC. This methylation signature shows promise as a future adjunctive screening test for thyroid nodules.