Polo-like kinase isoforms in breast cancer : expression patterns and prognostic implications

Polo-like kinase (PLK) family members are known to be functionally involved in mitotic signaling and in cytoskeletal reorganization in both normal and malignant cells. In this study, expression of PLK1 and PLK3 was determined immunohistochemically in tissue specimens of 135 breast carcinomas, and expression was correlated with clinicopathological parameters and patient prognosis. Strong PLK isoform overexpression was observed in 42.2% (PLK1) and 47.4% (PLK3) of breast carcinomas when compared with non-transformed breast tissue. A positive correlation of PLK isoform expression with tumor grade, vascular invasion, erbB2/HER-2 expression and markers of proliferative activity was evident. Additionally, an inverse correlation of PLK isoform expression and estrogen receptor status was observed. Overexpression of PLK3 but not of PLK1 was significantly linked to reduced median overall (P