Up-regulation of nuclear receptor coactivator amplified in breast cancer-1 in papillary thyroid carcinoma correlates with lymph node metastasis

Nuclear receptor coactivator amplified in breast cancer-1 (AIB1), a new oncogenic coactivator, is commonly overexpressed and amplified in variety of human cancers. However, the expression of AIB1 in papillary thyroid carcinoma (PTC), the major histologic type of thyroid cancer, and its clinical significance are still unclear.AIB1 expression in PTC was examined by immunohistochemistry using tissue microarrays comprised of 90 primary PTC, 46 matched lymph node, and 20 normal thyroid tissue specimens in this study.In the normal thyroid specimens, AIB1 expression was either absent or at low levels. In contrast, AIB1 overexpression was detected in 50 of 83 (60.2 %) primary PTC specimens. Up-regulated AIB1 was evident in 39 of 46 (73.5 %) matched lymph nodes. Overexpression of AIB1 was observed more frequently in PTCs with lymph node metastasis [N1a/N1b, 39/46 (73.5 %)] versus PTCs without lymph node metastasis [N0, 14/34 (41.2 %)]. Furthermore, high-level AIB1 expression was only observed in the lymph node-positive specimens. Moreover, we found no correlation between AIB1 expression and ER expression in PTC tissues.Our findings suggest that overexpression of AIB1 may be a biomarker for tumorigenesis and progression of PTC and may play an important role in its acquisition of a metastatic phenotype.