Comparative analysis of gene expression profiles of papillary thyroid microcarcinoma and papillary thyroid carcinoma

Papillary thyroid carcinomas (PTCs) measuring 1.0 cm or less were separately defined as papillary thyroid microcarcinomas (PTMs) by the World Health Organization, emphasizing on their benign behavior. However, some reported that PTMs may have aggressive behavior, can cause regional, or even distant metastases. But till now, the characteristics of PTMs were only reviewed and described by the clinicopathological parameters, and no analysis of PTM by the gene level is available. We report on the gene expression profiles of PTMs by the oligonucleotide microarrays and the results of comparative analysis with those of PTCs. The gene expression profiles of 25 pairs of PTMs and their normal thyroid tissue counterparts, and 11 pairs of PTCs and their normal counterparts, were analyzed by Affymetrix Human Genome U133A. Data were analyzed by the SAM and the DAVID 2008 program to detect differentially expressed genes in supervised sample classification. Two-hundred thirteen statistically significant up-regulated genes and -183 significant down-regulated genes of PTMs compared with their normal counterpart thyroid tissues, which were mainly cell adhesion-related genes and immune response genes, were detected. Two-hundred sixty-one up-regulated and -157 down-regulated genes of PTCs were also detected. In the comparative analyses of gene expression profiles of PTMs and PTCs, no significant difference was found. PTM should not be considered as the simple occult indolent thyroid cancer, but as the earlier stage of disease which eventually evolves into PTC, because the gene expression profiles of PTMs were not different from those of PTCs.