Association between p53-binding protein 1 expression and genomic instability in oncocytic follicular adenoma of the thyroid.

Oncocytic follicular adenomas (FAs) of the thyroid are neoplasms of follicular cell origin that are predominantly composed of large polygonal cells with eosinophilic and granular cytoplasm. However, the pathological characteristics of these tumors are largely unexplored. Both the initiation and progression of cancer can be caused by an accumulation of genetic mutations that can induce genomic instability. Thus, the aim of this study was to evaluate the extent of genomic instability in oncocytic FA. As the presence of p53-binding protein 1 (53BP1) in nuclear foci has been found to reflect DNA double-strand breaks that are triggered by various stresses, the immunofluorescence expression pattern of 53BP-1 was assessed in oncocytic and conventional FA. The association with the degree of DNA copy number aberration (CNA) was also evaluated using array-based comparative genomic hybridization. Data from this study demonstrated increased 53BP1 expression (i.e., "unstable" expression) in nuclear foci of oncocytic FA and a higher incidence of CNAs compared with conventional FA. There was also a particular focus on the amplification of chromosome 1p36 in oncocytic FA, which includes the locus for Tumor protein 73, a member of the p53 family implicated as a factor in the development of malignancies. Further evaluations revealed that unstable 53BP1 expression had a significant positive correlation with the levels of expression of Tumor protein 73. These data suggest a higher level of genomic instability in oncocytic FA compared with conventional FA, and a possible relationship between oncocytic FA and abnormal amplification of Tumor protein 73.