Immunohistochemical expression of homeoproteins Six1 and Pax3 in breast phyllodes tumours correlates with histological grade and clinical outcome

Aims Homeoproteins are transcription factors which critically regulate developmental processes. Deregulated expression of homeoproteins is observed in several malignancies, such as breast cancer and rhabdomyosarcoma, and contributes to malignant progression. We aimed to investigate the expression and prognostic importance of Six1 and Pax3 homeoproteins in phyllodes tumours – a group of uncommon biphasic tumours comprising both epithelial and stromal components. Methods and results A total of 272 cases diagnosed from January 2003 to December 2010 were included in this study – 189 (69.5%) benign, 60 (22.1%) borderline and 23 (8.4%) malignant tumours. Immunohistochemistry was performed on tissue microarray sections using antibodies against Six1 and Pax3. Staining H‐score was assessed in epithelium and stroma separately, and correlated with tumour grade, clinicopathological parameters and prognosis. Tumour grade was associated positively with stromal cytoplasmic expression (P