According to numerous published studies on thyroid cancers, the RASSF1A methylation and therefore silencing of gene expression correlated with more aggressive cancer phenotype/subtype—i.e., follicular, medullary, and undifferentiated forms (70–80%)—but was less often in PTC (15–63%) [30,51,52,53]. This evidence concerns the gene RASSF1 and thyroid cancer.