The precise mechanisms of tumorigenesis of breast cancer remains unknown in spite of major efforts. Recent studies have shown that High Mobility Group I (Y) Proteins [HMGI(Y)] have an important role in the regulation of chromatin structure and function, and that HMGI(Y) protein expression is generally correlated with a malignant phenotype. This study was undertaken to define the relationship of the HMGI(Y) protein expression between malignant breast tissue and non-malignant breast tissue in human, and clinico-pathologic findings were reviewed for this purpose.

Using Reverse Transcription-Polymerase Chain Reaction (RT-PCR) for HMGI(Y) with β-actin, this study demonstrated the expression of HMGI(Y). The p53, ER, and PRo were defined by immunohistochemical staining.

The HMGI(Y) expression was increased in the malignant tissue (90%), than in benign (76.9%) or normal (65%) tissue (p=0,031). As for the invasive ductal cancers, there was no difference between the HMGI(Y) expression and histopathologic parameters.

These results suggest that the HMGI(Y) expression may be of little pathogenetic prognostic importance in human breast cancer.